[media] v4l: vsp1: Fix race condition when stopping pipeline

When stopping the pipeline the driver waits for the pipeline state to be
set to VSP1_PIPELINE_STOPPED but fails to lock the pipe irqlock to read
the state variable protected by the lock. Fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>