[media] s5p-fimc: Don't allocate fimc-lite video device structure dynamically

This fixes potential invalid pointer de-reference, when
media_entity_cleanup() is called after video_unregister_device,
and video device structure memory is already freed.

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>