If the pipeline was already stopped when stopping the stream, no
frame end interrupt will be generated and the driver will time out
waiting for the pipeline to stop.

Fix this by setting the pipeline state to STOPPED when the pipeline is
idle waiting for frames to process, and to STOPPING at stream stop time
only when the pipeline is currently RUNNING.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>