compositor: change weston_surface::destroy_signal argument

Pass 'this' weston_surface as the data argument to
weston_surface::destroy_signal listeners. The old &surface->resource was
really just an offsetted pointer to the weston_surface anyway. And,
because 'resource' happened to be the first member in struct weston_surface,
it was actually 'this' weston_surface.

The argument type was accidentally changed in commit
26ed73cee858956f6af07c3e4bb49b5514f17b8b from wl_resource* to
wl_resource**.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/src/compositor.h b/src/compositor.h
index 5f49237..31ef5c7 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -883,7 +883,7 @@
 
 struct weston_surface {
 	struct wl_resource *resource;
-	struct wl_signal destroy_signal;
+	struct wl_signal destroy_signal; /* callback argument: this surface */
 	struct weston_compositor *compositor;
 
 	/** Damage in local coordinates from the client, for tex upload. */