Silence a valgrind warning

src/wayland-server.c

diff --git a/src/wayland-server.c b/src/wayland-server.c
index 4cb3dd5..f93aa64 100644
--- a/src/wayland-server.c
+++ b/src/wayland-server.c
@@ -461,7 +461,6 @@
 
 	interface = device->grab->interface;
 	interface->end(device->grab, time);
-	device->grab->input_device = NULL;
 	device->grab = NULL;
 
 	wl_list_remove(&device->grab_listener.link);