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.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>