[media] s5p-fimc: Prevent race conditions during subdevs registration

Make sure when fimc and fimc-lite capture video node is registered
it has valid pipeline_ops assigned to it. Otherwise when a video
node is opened right after is was registered there, might be an
attempt to use ops that are just being assigned, after function
v4l2_device_register_subdev() returns.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>