Fixed environment assignment for LCheckNonSmi.

This fixes browsing facebook.com with a debug version of Chrome.

TBR=ulan@chromium.org

Review URL: https://codereview.chromium.org/223763003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20476 ce2b1a6d-e550-0410-aec6-3dcde31c8c00