[llvm] [PowerPC] Fix assert which caused by PR 190606 (PR #194040)

[Lei Huang via llvm-commits]

================
@@ -15886,20 +15887,23 @@ SDValue PPCTargetLowering::combineSignExtendSetCC(SDNode *N,
 
   SDLoc dl(N);
   SelectionDAG &DAG = DCI.DAG;
-  EVT VT = N->getValueType(0);
   SDValue X = isNullConstant(LHS) ? RHS : LHS;
   EVT XVT = X.getValueType(); // The type of x in the setcc x, 0, eq.
 
+  if (!Subtarget.isPPC64() && XVT == MVT::i64)
----------------
lei137 wrote:

nit:
```suggestion
  if (XVT == MVT::i64 && !Subtarget.isPPC64())
```

https://github.com/llvm/llvm-project/pull/194040