compositor-drm: select the highest possible mode frequency

the mode list is ordered so that the lower frequencies come
before the higher ones, so traverse the list from the end
to the beginning

src/compositor-drm.c

@@ -1836,7 +1836,7 @@ create_output_for_connector(struct drm_compositor *ec,
 	current = NULL;
 	configured = NULL;
 
-	wl_list_for_each(drm_mode, &output->base.mode_list, base.link) {
+	wl_list_for_each_reverse(drm_mode, &output->base.mode_list, base.link) {
 		if (config == OUTPUT_CONFIG_MODE &&
 		    width == drm_mode->base.width &&
 		    height == drm_mode->base.height)