Fix x64 build.

TBR=whesse@chromium.org

Review URL: http://codereview.chromium.org/346012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3173 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/fast-codegen-x64.cc

@@ -678,7 +678,7 @@ void FastCodeGenerator::VisitBinaryOperation(BinaryOperation* expr) {
                                NO_OVERWRITE,
                                NO_GENERIC_BINARY_FLAGS);
       __ CallStub(&stub);
-      Move(expr->location(), kReturnRegister);
+      Move(expr->location(), rax);
 
       break;
     }