MIPS: Fix code for InstanceofStub.

Port r24654 (66aa0fb)

BUG=
R=dusan.milosavljevic@imgtec.com

Review URL: https://codereview.chromium.org/661803002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24667 ce2b1a6d-e550-0410-aec6-3dcde31c8c00