[media] v4l: vsp1: Don't validate links when the userspace API is disabled

As the pipeline is configured internally by the driver when the
userspace API is disabled its configuration can be trusted and link
validation isn't needed.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>