tty: n_gsm: fix redundant assignment of gsm->encoding

The function gsmld_open() contains a redundant assignment of gsm->encoding.
The same value of GSM_ADV_OPT is already assigned to it during the
initialization of the struct in gsm_alloc_mux() a few lines earlier.

Fix this by removing the redundant second assignment of gsm->encoding in
gsmld_open().

Fixes: e1eaea46 ("tty: n_gsm line discipline")
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20230420085017.7314-1-daniel.starke@siemens.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_gsm.c

@@ -3585,7 +3585,6 @@ static int gsmld_open(struct tty_struct *tty)
 	tty->receive_room = 65536;
 
 	/* Attach the initial passive connection */
-	gsm->encoding = GSM_ADV_OPT;
 	gsmld_attach_gsm(tty, gsm);
 
 	/* The mux will not be activated yet, we wait for correct