media: v4l: omap3isp: make v4l2_file_operations const

Make this const as it is only stored in a const field of a
video_device structure.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>