MIPS: Don't emit code for instructions that are hiding behind an HSoftDeoptimize

Port r13412 (36df819b)

BUG=
TEST=

Review URL: https://codereview.chromium.org/12022005
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13422 ce2b1a6d-e550-0410-aec6-3dcde31c8c00