[media] v4l: omap4iss: Stop started entities when pipeline start fails

If an entity can't be started when starting a pipeline we need to clean
up by stopping all entities that have been successfully started.
Otherwise the hardware and software states won't match, potentially
leading to crashes (for instance due to the CSI2 receiver receiving
interrupts with a NULL pipeline pointer).

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