Make the debug string for ISD::MERGE_VALUES consistent with the others.

llvm-svn: 37922
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 9eee198..9687a52 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3384,7 +3384,7 @@
   case ISD::CopyToReg:     return "CopyToReg";
   case ISD::CopyFromReg:   return "CopyFromReg";
   case ISD::UNDEF:         return "undef";
-  case ISD::MERGE_VALUES:  return "mergevalues";
+  case ISD::MERGE_VALUES:  return "merge_values";
   case ISD::INLINEASM:     return "inlineasm";
   case ISD::LABEL:         return "label";
   case ISD::HANDLENODE:    return "handlenode";