Fix bogus allocation limit in allocation folding.

R=ishell@chromium.org
TEST=mjsunit/allocation-folding

Review URL: https://codereview.chromium.org/73563004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17805 ce2b1a6d-e550-0410-aec6-3dcde31c8c00