media: rcar-vin: force default colorspace for media centric mode

The V4L2 specification clearly documents the colorspace fields as being
set by drivers for capture devices. Using the values supplied by
userspace thus wouldn't comply with the API. Until the API is updated to
allow for userspace to set these Hans wants the fields to be set by the
driver to fixed values.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>