Add a method to retrieve the media entity associated with a subdevice. The entityName() and deviceNode() methods are not needed anymore as they can be accessed through the media entity, remove them. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>