[media] return BUF_STATE_ERROR if streaming stopped during acquisition

When stop_streaming is called while a frame is currently being retrieved, the
buffer being filled will still be returned with BUF_STATE_DONE. By resetting
the sequence number and checking before returning the buffer, it can now
correctly be returned with BUF_STATE_ERROR.

Signed-off-by: Martin Kaltenbrunner <modin@yuri.at>
Signed-off-by: Florian Echtler <floe@butterbrot.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>