[clang] [LoopPeeling] Fix weights updating of peeled off branches (PR #70094)

[Matthias Braun via cfe-commits]

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

Seems like a sensible backstop for slightly incorrect profile data leading to extreme branch weights. Added some nitpicks, either way LGTM

https://github.com/llvm/llvm-project/pull/70094