clang-tidy: add ending namespace comments

Found with google-readability-namespace-comments

Signed-off-by: Rosen Penev <rosenp@gmail.com>

taglib/fileref.cpp

@@ -278,7 +278,7 @@ namespace
 
     return 0;
   }
-}
+}  // namespace
 
 class FileRef::FileRefPrivate : public RefCounter
 {