[llvm] [SCCP] get rid of potentially dangling iterator (PR #105609)

[Alexandros Lamprineas via llvm-commits]

labrinea wrote:

> > Hi, I am on vacation. I'll look at this next week. Thanks
> 
> Do you want to review this specifically? I can also send it to someone else.

I am happy either way

https://github.com/llvm/llvm-project/pull/105609