clients: destroy wl_registry on exit

Plug an insignificant memory leak in demo programs that bother to clean
up at all.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/clients/simple-shm.c b/clients/simple-shm.c
index 5bc26bf..831f9a4 100644
--- a/clients/simple-shm.c
+++ b/clients/simple-shm.c
@@ -369,6 +369,7 @@
 	if (display->compositor)
 		wl_compositor_destroy(display->compositor);
 
+	wl_registry_destroy(display->registry);
 	wl_display_flush(display->display);
 	wl_display_disconnect(display->display);
 	free(display);