media: imx: imx-mipi-csis: Don't stop streaming at runtime suspend time

Streaming is guaranteed to have been stopped by the time the device gets
runtime suspended, as pm_runtime_put() is called from .s_stream(0) only.
Drop the manual stop.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>