backend/x11: don't exit on dri3 DRM FD query failure

Even if the backend advertises dri3 support, querying the DRM FD may fail.
Instead of returning early, the backend creation process must continue because
shm might be supported.

backend/x11/backend.c

@@ -613,7 +613,8 @@ struct wlr_backend *wlr_x11_backend_create(struct wl_event_loop *loop,
 		x11->drm_fd = query_dri3_drm_fd(x11);
 		if (x11->drm_fd < 0) {
 			wlr_log(WLR_ERROR, "Failed to query DRI3 DRM FD");
-			goto error_event;
+			wlr_log(WLR_INFO, "Disabling DMA-BUF support");
+			x11->have_dri3 = false;
 		}
 	}