drm: Register connector instead of calling register_connector callback

drm_dp_mst_topology_mgr_cbs.register_connector callbacks are literally
identical amongst every driver and don't do anything other than
calling drm_connector_register(). Hence call drm_connector_register()
directly instead of a callback.

This is the preparatory step for removing the
drm_dp_mst_topology_mgr_cbs.register_connector callback hook.
Signed-off-by: Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>
Suggested-by: Emil Velikov <emil.velikov@collabora.com>
Suggested-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200307083023.76498-2-pankaj.laxminarayan.bharadiya@intel.comReviewed-by: Lyude Paul <lyude@redhat.com>

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -2178,7 +2178,7 @@ drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
 		drm_connector_set_tile_property(port->connector);
 	}
 
-	mgr->cbs->register_connector(port->connector);
+	drm_connector_register(port->connector);
 	return;
 
 error: