xwayland: stop direct accessing core struct member

Commit "weston-log: add function to avoid direct
access to compositor members in non-core code" added the
function weston_compositor_add_log_scope mainly to allow
libweston users to avoid direct accessing core structs, as
weston_compositor.

Replace weston_log_context_add_log_scope usage by
weston_compositor_add_log_scope.

Signed-off-by: Leandro Ribeiro <leandrohr@riseup.net>

xwayland/launcher.c

@@ -396,8 +396,7 @@ weston_module_init(struct weston_compositor *compositor)
 	}
 
 	wxs->wm_debug =
-		weston_log_ctx_add_log_scope(wxs->compositor->weston_log_ctx,
-					     "xwm-wm-x11",
+		weston_compositor_add_log_scope(wxs->compositor, "xwm-wm-x11",
 						"XWM's window management X11 events\n",
 						NULL, NULL, NULL);