media: imx: utils: Constify some mbus and ipu_image arguments

The imx_media_mbus_fmt_to_pix_fmt() and imx_media_mbus_fmt_to_ipu_image()
functions do not need to modify their mbus argument, and
imx_media_ipu_image_to_mbus_fmt() does not need to modify its ipu_image
argument. Make them const.

[slongerbeam@gmail.com: Constified mbus arg to
 imx_media_mbus_fmt_to_ipu_image(), and ipu_image
 arg to imx_media_ipu_image_to_mbus_fmt(), as well]

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>