compositor: Track pointer image protocol change

The request pointer.attach was replaced with pointer.set_cursor that
lets a client set the cursor surface for a given pointer.
diff --git a/clients/simple-egl.c b/clients/simple-egl.c
index cceca9e..25c7bdf 100644
--- a/clients/simple-egl.c
+++ b/clients/simple-egl.c
@@ -360,7 +360,7 @@
 	struct display *display = data;
 
 	if (display->window->fullscreen)
-		wl_pointer_attach(pointer, serial, NULL, 0, 0);
+		wl_pointer_set_cursor(pointer, serial, NULL, 0, 0);
 }
 
 static void