media: cx23885: add const to v4l2_file_operations structure

Declare v4l2_file_operations structure as const as it is only stored
in the fops field of video_device structure. This field is of type
const, so declare v4l2_file_operations structures with similar properties
as const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>