[llvm] [LoopVectorize] Fix cost model assert when vectorising calls (PR #125716)

[David Sherwood via llvm-commits]

david-arm wrote:

/cherry-pick https://github.com/llvm/llvm-project/commit/1930524bbde3cd26ff527bbdb5e1f937f484edd6 https://github.com/llvm/llvm-project/commit/3872e55758a5de035c032a975f244302c3ddacc3

https://github.com/llvm/llvm-project/pull/125716