tty: drop useless variable initialisation in tty_kopen()

The driver variable is assigned to unconditionally and not used before.
So there is no need to explicitly initialize it at the start of
tty_kopen().
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20191217075040.8020-1-u.kleine-koenig@pengutronix.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -1893,7 +1893,7 @@ static struct tty_driver *tty_lookup_driver(dev_t device, struct file *filp,
 struct tty_struct *tty_kopen(dev_t device)
 {
 	struct tty_struct *tty;
-	struct tty_driver *driver = NULL;
+	struct tty_driver *driver;
 	int index = -1;
 
 	mutex_lock(&tty_mutex);