[SelectionDAGBuilder] Use getPtrExtOrTrunc in place of getZExtOrTrunc. NFC

[craig.topper]

Summary

This getZExtOrTrunc seems to have been added when getPtrExtOrTrunc
was introduced. getPtrExtOrTrunc is currently equivalent to getZExtOrTrunc,
but could be changed for some target in the future.

[craig.topper]

Ping

[t.p.northover]

Looks reasonable.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

SDValue A = DAG.getNode(ISD::ADD, dl,
                             Flags);
 
     SDValue L = DAG.getLoad(MemVTs[i], dl, Root, A,
                             MachinePointerInfo(SV, Offsets[i]), Alignment,
                             MMOFlags, AAInfo, Ranges);
     Chains[ChainI] = L.getValue(1);
 
     if (MemVTs[i] != ValueVTs[i])
-      L = DAG.getZExtOrTrunc(L, dl, ValueVTs[i]);
+      L = DAG.getPtrExtOrTrunc(L, dl, ValueVTs[i]);
 
     Values[i] = L;
   }
 
   if (!ConstantMemory) {
     SDValue Chain = DAG.getNode(ISD::TokenFactor, dl, MVT::Other,
                                 ArrayRef(Chains.data(), ChainI));
     if (isVolatile)