[turbofan] Fix deoptimization of uint8, uint16 inputs.

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/707443003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25214 ce2b1a6d-e550-0410-aec6-3dcde31c8c00