[turbofan] More const-correctness changes.

src/compiler/simplified-operator-reducer.cc

Index: src/compiler/simplified-operator-reducer.cc
diff --git a/src/compiler/simplified-operator-reducer.cc b/src/compiler/simplified-operator-reducer.cc
index ac6153e25086e5fe1863f36ec3f703260a43a5b9..f05c345cefe2cf7baf822703ad51bccdf8f1f6e0 100644
--- a/src/compiler/simplified-operator-reducer.cc
+++ b/src/compiler/simplified-operator-reducer.cc
@@ -99,7 +99,7 @@ Reduction SimplifiedOperatorReducer::Reduce(Node* node) {
 
 
 Reduction SimplifiedOperatorReducer::Change(Node* node, Operator* op, Node* a) {
-  graph()->ChangeOperator(node, op);
+  node->set_op(op);
   node->ReplaceInput(0, a);
   return Changed(node);
 }