Merged r17451 into 3.22 branch.

MIPS: Fix uint32-to-smi conversion in Lithium.

BUG=chromium:309623
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/58103003

git-svn-id: https://v8.googlecode.com/svn/branches/3.22@17502 ce2b1a6d-e550-0410-aec6-3dcde31c8c00