backends/x11: Fix device hierarchy event handling for x11 backend

This commit adds the events created in the function
`meta_seat_x11_notify_devices` to the clutter events queue, which
are currently only added to the stage queue making the events not
being picked up by the `clutter_seat_handle_event_post` function.
This results in devices not getting added to the device-list of
`MetaInputSettings`.

Fixes the bug in which mouse and touchpad settings are not working in
the settings app during x11 session.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1767>

src/backends/x11/meta-seat-x11.c

@@ -1346,7 +1346,8 @@ meta_seat_x11_notify_devices (MetaSeatX11  *seat_x11,
       event = clutter_event_new (CLUTTER_DEVICE_ADDED);
       clutter_event_set_device (event, device);
       clutter_event_set_stage (event, stage);
-      clutter_do_event (event);
+      clutter_event_put (event);
+      clutter_event_free (event);
     }
 }