[CodeGen] ProcessSDDbgValues - use const-ref value in for-range loop. NFCI.

Avoid unnecessary copies, reported by MSVC static analyzer.

Author: RKSimon

llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp

@@ -742,7 +742,7 @@ ProcessSDDbgValues(SDNode *N, SelectionDAG *DAG, InstrEmitter &Emitter,
   /// Returns true if \p DV has any VReg operand locations which don't exist in
   /// VRBaseMap.
   auto HasUnknownVReg = [&VRBaseMap](SDDbgValue *DV) {
-    for (SDDbgOperand L : DV->getLocationOps()) {
+    for (const SDDbgOperand &L : DV->getLocationOps()) {
       if (L.getKind() == SDDbgOperand::SDNODE &&
           VRBaseMap.count({L.getSDNode(), L.getResNo()}) == 0)
         return true;