Fix the VC GenXPacketizer pass to work with opaque pointers

The GenXPacketizer pass missed the uniform load result handling, when
opaque pointers are used. This caused assertion failures during
packetization and incorrect code generation.

Author: vmustya

IGC/VectorCompiler/lib/GenXOpts/CMPacketize/GenXPacketize.cpp

@@ -618,6 +618,7 @@ void GenXPacketize::findUniformInsts(Function &F) {
       const Value *Use = (*UI);
       if (auto *LI = dyn_cast<LoadInst>(Use)) {
         UniformInsts.insert(LI);
+        UVSet.push((Value *)LI);
       } else if (auto *GEP = dyn_cast<GetElementPtrInst>(Use)) {
         if (GEP->getPointerOperand() == Def) {
           UniformInsts.insert(GEP);