tty: n_gsm: remove redundant pointer gsm

Pointer gsm is assigned a value that is never read, hence it is
redundant and can be removed. Cleans up clang warning:

drivers/tty/n_gsm.c:2979:2: warning: Value stored to 'gsm' is never read
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_gsm.c

@@ -2955,7 +2955,6 @@ static int gsmtty_open(struct tty_struct *tty, struct file *filp)
 static void gsmtty_close(struct tty_struct *tty, struct file *filp)
 {
 	struct gsm_dlci *dlci = tty->driver_data;
-	struct gsm_mux *gsm;
 
 	if (dlci == NULL)
 		return;
@@ -2964,7 +2963,6 @@ static void gsmtty_close(struct tty_struct *tty, struct file *filp)
 	mutex_lock(&dlci->mutex);
 	gsm_destroy_network(dlci);
 	mutex_unlock(&dlci->mutex);
-	gsm = dlci->gsm;
 	if (tty_port_close_start(&dlci->port, tty, filp) == 0)
 		return;
 	gsm_dlci_begin_close(dlci);