[llvm-readobj] - Fix a warning.

This addresses post review comment for D92018.

The warning was:

```
error: loop variable 'Note' is always a copy because the range of type 'iterator_range<llvm::object::ELFFile<llvm::object::ELFType<llvm::support::big, true> >::Elf_Note_Iterator>' (aka 'iterator_range<Elf_Note_Iterator_Impl<ELFType<(llvm::support::endianness)0U, true> > >') does not return a reference [-Werror,-Wrange-loop-analysis]
      for (const typename ELFT::Note &Note : Obj.notes(S, Err))
```