simple-touch: use proper damage in touch_paint()

Should reduce update overhead.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/clients/simple-touch.c b/clients/simple-touch.c
index f8afbb0..6087fe4 100644
--- a/clients/simple-touch.c
+++ b/clients/simple-touch.c
@@ -141,7 +141,7 @@
 	p += touch->width;
 	p[2] = c;
 
-	wl_surface_damage(touch->surface, 0, 0, touch->width, touch->height);
+	wl_surface_damage(touch->surface, x - 2, y - 2, 5, 5);
 }
 
 static void