[media] V4L: omap1-camera: fix Oops with NULL platform data

Consistently check for platform data != NULL before dereferencing.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>