[media] media: blackfin: bfin_capture: make sure all buffers are returned on stop_streaming() callback

In start_streaming() callback the buffer is removed from the
dma_queue list and assigned to cur_frm, this patch makes sure
that is returned to vb2 core with VB2_BUF_STATE_ERROR flag.
Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Tested-by: Scott Jiang <scott.jiang.linux@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>