[llvm] [BOLT] Avoid repeated hash lookups (NFC) (PR #140426)

[Amir Ayupov via llvm-commits]

https://github.com/aaupov approved this pull request.

Thank you for the cleanup. We have similar helpers in `DataReader::parse` – would you mind covering them as well?

https://github.com/llvm/llvm-project/pull/140426