[turbofan] Fix branch hints for ChangeInt32ToTagged and ChangeTaggedToUI32.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/694353006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25106 ce2b1a6d-e550-0410-aec6-3dcde31c8c00