A64: Replace a Subs by a Sub where flags don't need to be updated.

R=jochen@chromium.org

Review URL: https://codereview.chromium.org/170553002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19529 ce2b1a6d-e550-0410-aec6-3dcde31c8c00