fbdev: au1100fb: Drop if with an always false condition

The driver core never calls a remove callback with the platform_device
pointer being NULL. So the check for this condition can just be dropped.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Helge Deller <deller@gmx.de>