compositor: Use pixman_region32_intersect_rect() instead of temp region

We avoid reusing 'opaque' and don't leak the region.

src/compositor.c

@@ -1262,13 +1262,12 @@ surface_commit(struct wl_client *client, struct wl_resource *resource)
 	surface->pending.sy = 0;
 
 	/* wl_surface.damage */
-	pixman_region32_init_rect(&opaque, 0, 0,
-				  surface->geometry.width,
-				  surface->geometry.height);
 	pixman_region32_union(&surface->damage, &surface->damage,
 			      &surface->pending.damage);
-	pixman_region32_intersect(&surface->damage, &surface->damage,
+	pixman_region32_intersect_rect(&surface->damage, &surface->damage,
-				  &opaque);
+				       0, 0,
+				       surface->geometry.width,
+				       surface->geometry.height);
 	empty_region(&surface->pending.damage);
 
 	/* wl_surface.set_opaque_region */