[media] solo6x10: clean up properly in stop_streaming

This fixes warning from drivers/media/v4l2-core/videobuf2-core.c,
WARN_ON(atomic_read(&q->owned_by_drv_count)).

Signed-off-by: Andrey Utkin <andrey.krieger.utkin@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>