[GlobalISel] Fix buildZExtInReg creating new register.

[vangthao]

Summary

Fix a bug where buildZExtInReg will create and use a new register instead of using the register from parameter DstOp Res.

[foad]

Thanks!

llvm/lib/CodeGen/GlobalISel/MachineIRBuilder.cpp

 }
 
 MachineInstrBuilder MachineIRBuilder::buildZExtInReg(const DstOp &Res,
                                                      const SrcOp &Op,
                                                      int64_t ImmOp) {
   LLT ResTy = Res.getLLTTy(*getMRI());
   auto Mask = buildConstant(
       ResTy, APInt::getLowBitsSet(ResTy.getScalarSizeInBits(), ImmOp));
-  return buildAnd(ResTy, Op, Mask);
+  return buildAnd(Res, Op, Mask);
 }
 
 MachineInstrBuilder MachineIRBuilder::buildCast(const DstOp &Dst,
                                                 const SrcOp &Src) {
   LLT SrcTy = Src.getLLTTy(*getMRI());
   LLT DstTy = Dst.getLLTTy(*getMRI());
   if (SrcTy == DstTy)
     return buildCopy(Dst, Src);