Fix GEP lowering pass in VC

The `ptrtoint` folding function should take care of `<1 x ptr>` bitcast
to and from `ptr`.

(cherry picked from commit 8f2dbaf)

Author: vmustya

IGC/VectorCompiler/lib/GenXCodeGen/GenXGEPLowering.cpp

@@ -194,9 +194,9 @@ Value *GenXGEPLowering::visitGetElementPtrInst(GetElementPtrInst &GEP) {
   }
 
   PointerValue = Builder->CreatePtrToInt(PtrOp, IntPtrTy);
-  auto *PTI = dyn_cast<PtrToIntInst>(PointerValue);
-  if (auto *NewPTI = visitPtrToIntInst(*PTI))
-    PointerValue = NewPTI;
+  if (auto *PTI = dyn_cast<PtrToIntInst>(PointerValue))
+    if (auto *NewPTI = visitPtrToIntInst(*PTI))
+      PointerValue = NewPTI;
 
   unsigned PtrMathSizeInBits =
       DL->getPointerSizeInBits(PtrTy->getAddressSpace());