[llvm] [NFC][LLVM] Code cleanup in CloneFunction.cpp (PR #162875)

[Jeremy Morse via llvm-commits]

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

LGTM in general; I usually prefer explicit types over `auto` where it's not a burden to name the type, so this is a good change for me. Best to leave this a day before merging though just in case there are other style expectations out there.

https://github.com/llvm/llvm-project/pull/162875