Fix broken build by removing more const qualifiers.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
===================================================================
--- src/hydrogen-instructions.cc	(revision 6866)
+++ src/hydrogen-instructions.cc	(working copy)
@@ -928,7 +928,7 @@
 }
 
 
-HValue* HPhi::GetRedundantReplacement() const {
+HValue* HPhi::GetRedundantReplacement() {
   HValue* candidate = NULL;
   int count = OperandCount();
   int position = 0;