MIPS: Fix if condition in DoTransitionElementsKind.

This commit fixes a couple of mjsunit test failures in debug mode,
which were introduced by commit r11636 (fe0c6bbe).

BUG=
TEST=

Review URL: https://codereview.chromium.org/11941004
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13420 ce2b1a6d-e550-0410-aec6-3dcde31c8c00