media: v4l2-mem2mem: Fix hold buf flag checks

Hold buf flag is set on output queue, not capture. Fix that.

Fixes: f07602ac ("media: v4l2-mem2mem: add new_frame detection")
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>