[media] videobuf2-core: fill in length field for multiplanar buffers

length should be set to num_planes in __fill_v4l2_buffer(). That way the
caller knows how many planes there are in the buffer.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/v4l2-core/videobuf2-core.c

@@ -348,6 +348,7 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b)
 		 * Fill in plane-related data if userspace provided an array
 		 * for it. The caller has already verified memory and size.
 		 */
+		b->length = vb->num_planes;
 		memcpy(b->m.planes, vb->v4l2_planes,
 			b->length * sizeof(struct v4l2_plane));
 	} else {