backend/drm: add wlr_drm_connector_state.connector

Will be useful for multi-connector commits, to avoid having to
pass the list of connectors separately from their state.

backend/drm/drm.c

@@ -505,6 +505,7 @@ static void drm_connector_state_init(struct wlr_drm_connector_state *state,
 		struct wlr_drm_connector *conn,
 		const struct wlr_output_state *base) {
 	*state = (struct wlr_drm_connector_state){
+		.connector = conn,
 		.base = base,
 		.modeset = base->allow_reconfiguration,
 		.active = output_pending_enabled(&conn->output, base),

include/backend/drm/drm.h

@@ -123,6 +123,7 @@ struct wlr_drm_mode {
 };
 
 struct wlr_drm_connector_state {
+	struct wlr_drm_connector *connector;
 	const struct wlr_output_state *base;
 	bool modeset;
 	bool nonblock;