message: Fix another occurrence of needing to use member accessors.
diff: @@ -746,8 +746,8 @@ private:
  int MatchAttributeIndex(llvm::StringRef attribute_name) const {
  for (const auto &Item : llvm::enumerate(s_filter_attributes)) {
  - if (attribute_name == Item.Value)
  - return Item.Index;
  + if (attribute_name == Item.value())
  + return Item.index();
  }
  // We didn't match anything.
  