[llvm] [PowerPC] Avoid repeated hash lookups (NFC) (PR #131724)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `amdgpu-offload-rhel-9-cmake-build-only` running on `rocm-docker-rhel-9` while building `llvm` at step 3 "checkout".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/205/builds/3816

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 3 (checkout) failure: update (failure)
git version 2.43.5
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
fatal: expected flush after ref listing

```

</details>

https://github.com/llvm/llvm-project/pull/131724