media: imx: imx7-media-csi: Get rid of superfluous call to imx7_csi_mbus_fmt_to_pix_fmt

There is no need to convert input pixformat to mbus_framefmt and back
again. Instead apply pixformat width constrains directly.
Assign compose values before adjusting pixformat height/width.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>