[media] s5k5baf: Check v4l2_of_parse_endpoint() return value

The v4l2_of_parse_endpoint() function can fail so check the return value.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>