V4L/DVB (10066): mt9m001 mt9v022: fix bus-width switch GPIO availability test

Testing for non-NULL platform-data is not enough, we have to check if the GPIO
in the platform data is valid or not. Also see my earlier patch:

	[ARM] pxa/pcm990: use negative number for an invalid GPIO in camera data

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>