Added missing const from my last commit.

llvm-svn: 172736
diff --git a/llvm/lib/Transforms/Scalar/ObjCARC.cpp b/llvm/lib/Transforms/Scalar/ObjCARC.cpp
index a54bd2b..8dae235 100644
--- a/llvm/lib/Transforms/Scalar/ObjCARC.cpp
+++ b/llvm/lib/Transforms/Scalar/ObjCARC.cpp
@@ -170,7 +170,7 @@
 
   raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class)
      LLVM_ATTRIBUTE_USED;
-  raw_ostream &operator<<(raw_ostream &OS, InstructionClass Class) {
+  raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class) {
     switch (Class) {
     case IC_Retain:
       return OS << "IC_Retain";