s390/ccwgroup: Drop if with an always false condition

The driver core only calls a bus remove callback when there is a driver.
So dev->driver is never NULL and the check can safely be removed.

Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20210713193522.1770306-4-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>