backend/session: Close fd in wlr_session_close_file

This was lost in the session_impl removal refactor.

backend/session/session.c

@@ -310,6 +310,7 @@ void wlr_session_close_file(struct wlr_session *session,
 	if (libseat_close_device(session->seat_handle, dev->device_id) == -1) {
 		wlr_log_errno(WLR_ERROR, "Failed to close device %d", dev->device_id);
 	}
+	close(dev->fd);
 	wl_list_remove(&dev->link);
 	free(dev);
 }