tty: n_gsm: remove obsolete mknod doc example

The n_gsm driver handles registration of /dev/gsmttyX nodes, so there's
no need to do mknod manually.

Signed-off-by: Martin Hundebøll <martin@geanix.com>
Link: https://lore.kernel.org/r/20190710192656.60381-1-martin@geanix.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/driver-api/serial/n_gsm.rst

@@ -63,24 +63,14 @@ Major parts of the initialization program :
 	daemon(0,0);
 	pause();
 
-4. create the devices corresponding to the "virtual" serial ports (take care,
-   each modem has its configuration and some DLC have dedicated functions,
-   for example GPS), starting with minor 1 (DLC0 is reserved for the management
-   of the mux)::
-
-     MAJOR=`cat /proc/devices |grep gsmtty | awk '{print $1}`
-     for i in `seq 1 4`; do
-	mknod /dev/ttygsm$i c $MAJOR $i
-     done
-
-5. use these devices as plain serial ports.
+4. use these devices as plain serial ports.
 
    for example, it's possible:
 
    - and to use gnokii to send / receive SMS on ttygsm1
    - to use ppp to establish a datalink on ttygsm2
 
-6. first close all virtual ports before closing the physical port.
+5. first close all virtual ports before closing the physical port.
 
    Note that after closing the physical port the modem is still in multiplexing
    mode. This may prevent a successful re-opening of the port later. To avoid