kern: fix warn-errors

libraries/libmesosphere/include/mesosphere/kern_k_light_server_session.hpp

@@ -41,7 +41,7 @@ namespace ams::kern {
             }
 
             virtual void Destroy() override;
-            static void PostDestroy(uintptr_t arg) { /* ... */ }
+            static void PostDestroy(uintptr_t arg) { MESOSPHERE_UNUSED(arg); /* ... */ }
 
             constexpr const KLightSession *GetParent() const { return this->parent; }