x64 BinaryOpStub::GenerateSmiCode use wrong registers in one code path.

e.g. d8 --trace_ic
var dd = new Float64Array(2);
dd[1] = 1;
(function fn() {
  for (var i = 0; i < 1000; i++)
  dd[0] = 2 / dd[1];
})();
It keeps falling into runtime call and patching.

No regression test, because I don't how to test it.

Review URL: https://chromiumcodereview.appspot.com/10834064
Patch from Zheng Liu <shdwthr@gmail.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12226 ce2b1a6d-e550-0410-aec6-3dcde31c8c00