MIPS: Fixed spec violation of storing to length of a frozen object.

Port r20005 (d647ec2)

BUG=chromium:350890
LOG=N
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/202063003

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20013 ce2b1a6d-e550-0410-aec6-3dcde31c8c00