media: sun4i_csi: Don't use v4l2_subdev_link_validate() for video device

media: sun4i_csi: Don't use v4l2_subdev_link_validate() for video device

The v4l2_subdev_link_validate() function is a helper designed to
validate links whose sink is a subdev. When called on a link whose sink
is a video device, it only prints a warning and returns. Its usage in
the sun4i_csi driver is wrong, leaving the link from the sub4i_csi
subdev to the capture video device unvalidated.

Planned improvements to the v4l2_subdev_link_validate() function will
turn the warning into an error, breaking the sun4i_csi driver. As an
interim measure, move the warning to the sun4i_csi driver in a custom
validation handler, and drop the call to the helper.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>