[media] rcar-vin: refactor and fold in function after stall handling rework

With the driver stopping and starting the stream each time the driver is
stalled rvin_capture_off() can be folded in to the only caller.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>