media: staging: media: use relevant lock

The data protected is video_out2 and the lock that is released is
&video_out2->dma_queue_lock, so it seems that that lock should be
taken as well.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>