MIPS: Fix cctest/NaNs after r23767 "Replace our home-grown BitCast with bit_cast from Chrome/Google3".

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/548283002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23779 ce2b1a6d-e550-0410-aec6-3dcde31c8c00