[media] v4l: Don't warn during link validation when encountering a V4L2 devnode

v4l2_subdev_link_validate_get_format() retrieves the remote pad format
depending on the entity type and prints a warning if the entity type is
not supported. The type check doesn't take the subtype into account, and
thus always prints a warning for device node types, even when supported.
Fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>