MIPS: Fix usage of EmitBranch in compare-minus-zero-and-branch.

Port r17669 (132efad)

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/71003003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17675 ce2b1a6d-e550-0410-aec6-3dcde31c8c00