clang-tidy: namespace comment

Found with llvm-namespace-comment

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

taglib/dsdiff/dsdifffile.cpp

@@ -81,7 +81,7 @@ namespace
     PROPChunk = 0,
     DIINChunk = 1
   };
-}
+} // namespace
 
 class DSDIFF::File::FilePrivate
 {