media: staging: imx-csi: use media_pad_is_streaming helper

media: staging: imx-csi: use media_pad_is_streaming helper

The media_pad_is_streaming() helper is explicitly intended to check whether
a pad has been started with media_pipeline_start(). Use it instead of
relying on the implicit assumption that a pad with a pipeline is streaming.

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>