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

[via llvm-commits]

================
@@ -9207,7 +9205,8 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
     if (!PhiR)
       continue;
 
-    const RecurrenceDescriptor &RdxDesc = PhiR->getRecurrenceDescriptor();
+    const RecurrenceDescriptor &RdxDesc = Legal->getRecurrenceDescriptor(
+        cast<PHINode>(PhiR->getUnderlyingInstr()));
----------------
ayalz wrote:

```suggestion
    RecurKind RecurrenceKind = PhiR->getRecurrenceKind();
    const RecurrenceDescriptor &RdxDesc = Legal->getRecurrenceDescriptor(
        cast<PHINode>(PhiR->getUnderlyingInstr()));
```
and replace `RdxDesc.getRecurrenceKind()` below with `RecurrenceKind`?

Getting rid of RdxDesc here is more difficult: in addition to capturing RdxDesc's FMF in PhiR, code below also uses RdxDesc to retrieve sentinel value, recurrence type, isSigned, Loop Exit Instr, ... ?

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