[llvm] [VPlan] Fold VPDef into VPRecipeBase (NFC). (PR #174282)

[via llvm-commits]

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@@ -212,10 +210,13 @@ class VPRecipeValue : public VPValue {
   friend class VPValue;
   friend class VPDef;
   /// Pointer to the VPDef that defines this VPValue.
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ayalz wrote:

```suggestion
  /// Pointer to the VPRecipeBase that defines this VPValue.
```

https://github.com/llvm/llvm-project/pull/174282