compositor: free region members on surface destroy

The two pixman regions of struct wlsc_surface were not being freed
properly.

Fixes some Valgrind errors.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/compositor/compositor.c b/compositor/compositor.c
index c3211e5..d710d5f 100644
--- a/compositor/compositor.c
+++ b/compositor/compositor.c
@@ -367,6 +367,9 @@
 
 	wl_list_remove(&surface->buffer_link);
 
+	pixman_region32_fini(&surface->damage);
+	pixman_region32_fini(&surface->opaque);
+
 	free(surface);
 }