The link_validate pad op will only be called on sink pads. Document this.
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: NJacopo Mondi <jacopo@jmondi.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab+huawei@kernel.org>