gpio: mc33880: Drop if with an always false condition

An spi remove callback is only called for devices that probed
successfully. In this case this implies that mc33880_probe() set a
non-NULL driver data. So the check for mc being NULL is never true and
the check can be dropped.

Also the return value ofspi remove callbacks is ignored anyway.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>