[media] coda: dequeue buffers on streamoff

This is needed to decrease the q->owned_by_drv_count to zero before
__vb2_queue_cancel is called, to avoid the WARN_ON therein.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>