[media] V4L: videobuf2: update buffer state on VIDIOC_QBUF

V4L2 specification states, that the videobuffer state flags have to be
updated on VIDIOC_QBUF ioctl(). Videobuf2 currently doesn't do that,
which is fixed by this patch.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>