[llvm] [LV][NFC] Refactor code for extracting first active element (PR #131118)

[Florian Hahn via llvm-commits]

================
@@ -880,6 +888,8 @@ bool VPInstruction::onlyFirstLaneUsed(const VPValue *Op) const {
     return false;
   case Instruction::PHI:
     return true;
+  case Instruction::ExtractElement:
+    return Op == getOperand(1);
----------------
fhahn wrote:

```suggestion
    return false;
 case Instruction::ExtractElement:
    return Op == getOperand(1);
  case Instruction::PHI:
    return true;
```

nit: might be good to loosely try to keep things ordered 

https://github.com/llvm/llvm-project/pull/131118