Use correct syntax markup for shell

Approved by:	carlavilla

documentation/content/en/articles/serial-uart/_index.adoc

@@ -528,7 +528,7 @@ COMTEST can be used as a screening tool to alert the administrator to the presen
 
 If you run COMTEST on a 16550 that is in a modem or a modem is attached to the serial port, you need to first issue a ATE0&W command to the modem so that the modem will not echo any of the test characters. If you forget to do this, COMTEST will report at least this one difference:
 
-[source,bash]
+[source,shell]
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 Error (6)...Timeout interrupt failed: IIR = c1  LSR = 61
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@@ -774,7 +774,7 @@ The flags entry _must_ be changed from this example unless you are using the exa
 indicates that the master port is sio16. If I added another board and assigned sio17 through sio28, the flags for all 16 ports on _that_ board would be 0x1C05, where 1C indicates the minor number of the master port. Do not change the 05 setting.
 . Save and complete the kernel configuration, recompile, install and reboot. Presuming you have successfully installed the recompiled kernel and have it set to the correct address and IRQ, your boot message should indicate the successful probe of the Boca ports as follows: (obviously the sio numbers, IO and IRQ could be different)
 +
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+[source,shell]
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 sio1 at 0x100-0x107 flags 0x1005 on isa
 sio1: type 16550A (multiport)
@@ -812,7 +812,7 @@ sio16: type 16550A (multiport master)
 + 
 If the messages go by too fast to see, 
 +
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+[source,shell]
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 # dmesg | more
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@@ -821,7 +821,7 @@ will show you the boot messages.
 + 
 If you do need to create the [.filename]#/dev# entries, run the following as `root`:
 +
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+[source,shell]
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 # cd /dev
 # ./MAKEDEV tty1
@@ -835,7 +835,7 @@ If you do need to create the [.filename]#/dev# entries, run the following as `ro
 If you do not want or need call-out devices for some reason, you can dispense with making the [.filename]#cua*# devices.
 . If you want a quick and sloppy way to make sure the devices are working, you can simply plug a modem into each port and (as root) 
 +
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+[source,shell]
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 # echo at > ttyd*
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@@ -899,7 +899,7 @@ device          sio2    at isa? port "IO_COM3" flags 0x205 irq 3
 
 Note that the `flags` setting for [.filename]#sio1# and [.filename]#sio2# is truly essential; refer to man:sio[4] for details. (Generally, the `2` in the "flags" attribute refers to [.filename]#sio#`2` which holds the IRQ, and you surely want a `5` low nibble.) With kernel verbose mode turned on this should yield something similar to this:
 
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+[source,shell]
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 sio0: irq maps: 0x1 0x11 0x1 0x1
 sio0 at 0x3f8-0x3ff irq 4 flags 0x10 on isa
@@ -932,7 +932,7 @@ device cy0 at isa? irq 10 iomem 0xd4000 iosiz 0x2000
 . Rebuild and install the new kernel.
 . Make the device nodes by typing (the following example assumes an 8-port board):
 +
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+[source,shell]
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 # cd /dev
 # for i in 0 1 2 3 4 5 6 7;do ./MAKEDEV cuac$i ttyc$i;done
@@ -996,7 +996,7 @@ The following step, is not necessary if you are using man:devfs[5] in FreeBSD 5.
 
 After rebooting with the new kernel, you need to make the device nodes in [.filename]#/dev#. The [.filename]#MAKEDEV# script will take care of this for you. Count how many total ports you have and type:
 
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+[source,shell]
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 # cd /dev
 # ./MAKEDEV ttyAnn cuaAnn