MIPS64: Fix ConvertDToI test.

TEST=cctest/test-code-stubs-mips64/ConvertDToI
BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/616853004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24372 ce2b1a6d-e550-0410-aec6-3dcde31c8c00