media: imx: imx7-media-csi: Set the MIPI data type based on the bus code

The MIPI CSI-2 data type depends solely on the media bus code on the
sink pad. Deriving it from the pixel format is confusing. Simplify the
code.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>