[llvm] [VPlan] Replace RdxDesc with RecurKind in VPReductionPHIRecipe (NFC). (PR #142322)

[via llvm-commits]

================
@@ -8310,7 +8307,7 @@ VPRecipeBase *VPRecipeBuilder::tryToCreateWidenRecipe(VPSingleDefRecipe *R,
       unsigned ScaleFactor =
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ayalz wrote:

Above
```
      const RecurrenceDescriptor &RdxDesc =
          Legal->getReductionVars().find(Phi)->second;
```
can be replaced (independently) with
```
      const RecurrenceDescriptor &RdxDesc =
          Legal->getRecurrenceDescriptor(Phi);
```
?

Similar candidates in
`LoopVectorizationCostModel::collectElementTypesForWidening()`, `LoopVectorizationCostModel::getReductionPatternCost()`.

https://github.com/llvm/llvm-project/pull/142322