Clarify the behavior of v4l2_buffer in the multiplanar case,
including fixing a false statement: you can't set m.planes to NULL
when calling DQBUF.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>