X87: Fix a typo in below CL

r21515 (6d0ec9a)
Convert ElementsKind into a BitField

BUG=
R=danno@chromium.org

Review URL: https://codereview.chromium.org/301563008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21551 ce2b1a6d-e550-0410-aec6-3dcde31c8c00