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

[via llvm-commits]

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@@ -9428,7 +9427,7 @@ void VPWidenMemoryInstructionRecipe::execute(VPTransformState &State) {
                                          nullptr, "wide.masked.gather");
       State.addMetadata(NewLI, LI);
     } else {
-      auto *VecPtr = State.get(getAddr(), Part);
+      auto *VecPtr = State.get(getAddr(), VPIteration(Part, 0));
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ayalz wrote:

```suggestion
      auto *VecPtr = State.get(getAddr(), Part, true /* scalar */);
```

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