[llvm] [VPlan] Consistently use (Part, 0) for first lane scalar values (PR #80271)

[via llvm-commits]

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@@ -1640,7 +1649,7 @@ void VPCanonicalIVPHIRecipe::execute(VPTransformState &State) {
   EntryPart->addIncoming(Start, VectorPH);
   EntryPart->setDebugLoc(getDebugLoc());
   for (unsigned Part = 0, UF = State.UF; Part < UF; ++Part)
-    State.set(this, EntryPart, Part);
+    State.set(this, EntryPart, VPIteration(Part, 0));
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ayalz wrote:

```suggestion
    State.set(this, EntryPart, Part, true /* scalar */);
```

https://github.com/llvm/llvm-project/pull/80271