MIPS: Only to the relevant checks in LoadFunctionPrototype.

Port r22550 (c5209a6)

BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/416513002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22566 ce2b1a6d-e550-0410-aec6-3dcde31c8c00