MIPS: Reland "Fixed environment assignment for LCheckNonSmi."

Port r20495 (705b65bc)

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/225023007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20518 ce2b1a6d-e550-0410-aec6-3dcde31c8c00