input-settings/x11: Only warn once about missing udev support

Otherwise we end up logging the same message everytime we enter this function,
flooding the logs and making it annoying to spot other entries.

src/backends/x11/meta-input-settings-x11.c

@@ -488,7 +488,14 @@ has_udev_property (MetaInputSettings  *settings,
   g_object_unref (parent_udev_device);
   return FALSE;
 #else
+  static gboolean warned_once = FALSE;
+
+  if (!warned_once)
+    {
       g_warning ("Failed to set acceleration profile: no udev support");
+      warned_once = TRUE;
+    }
+
   return FALSE;
 #endif
 }