[llvm] [NFC][IR2Vec] Change getSlotIndex parameter from Value* to Value& (PR #155700)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

@svkeerthy This is stuck in a rebase loop. You probably want to cancel the merge in Graphite and restart it once CI has completed.

https://github.com/llvm/llvm-project/pull/155700