media: i2c: ds90ub913: Stop accessing streams configs directly

media: i2c: ds90ub913: Stop accessing streams configs directly

The v4l2_subdev_stream_config structure will be made private. Stop
accessing it directly, iterate over routes instead to initialize
formats.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>