[SimplifyCFG] Avoid use of ConstantExpr::getIntegerCast() (NFC)

We're working on a ConstantInt here, so constant folding will
always succeed. Just avoid using the ConstantExpr API.

Author: nikic

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -502,7 +502,7 @@ static ConstantInt *GetConstantInt(Value *V, const DataLayout &DL) {
           return CI;
         else
           return cast<ConstantInt>(
-              ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
+              ConstantFoldIntegerCast(CI, PtrTy, /*isSigned=*/false, DL));
       }
   return nullptr;
 }