Fix x64 breakage in r3136.

Make sure that the return value is moved to rax. The line added back was accidently removed in r3136.

TBR=lrn@chromium.org
Review URL: http://codereview.chromium.org/339021

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3140 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/codegen-x64.cc

@@ -5235,6 +5235,7 @@ void DeferredInlineSmiAddReversed::Generate() {
 void DeferredInlineSmiSub::Generate() {
   GenericBinaryOpStub igostub(Token::SUB, overwrite_mode_, NO_SMI_CODE_IN_STUB);
   igostub.GenerateCall(masm_, dst_, value_);
+  if (!dst_.is(rax)) __ movq(dst_, rax);
 }