ia32: Restore missing temp register for LNumberTagU

BUG=v8:2692
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/17865002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15334 ce2b1a6d-e550-0410-aec6-3dcde31c8c00