[llvm] [LV] Fix incorrect cost kind in VPReplicateRecipe::computeCost (PR #153216)

[David Sherwood via llvm-commits]

david-arm wrote:

> Thanks. Would be great to have a test case for this. I can check if I can surface anything

I don't think this is even possible at the moment, because this will currently only apply if you build with `-Oz -fvectorize`, but you can't even write a test case for this because we hit the error at the end of `LoopVectorizationCostModel::computeMaxVF`:

```
  reportVectorizationFailure(
      "Cannot optimize for size and vectorize at the same time.",
```

I suppose that really means this patch is NFC and should be harmless. I just wanted to change the CostKind for completeness.

https://github.com/llvm/llvm-project/pull/153216