Fix LStoreCodeEntry to treat the code_object parameter as input.

The bug seems to trigger only with array_index_dehoisting off in
the snapshot, so it is hard to test for (ideas?).

R=mvstanton@chromium.org
BUG=

Review URL: https://codereview.chromium.org/347523002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21885 ce2b1a6d-e550-0410-aec6-3dcde31c8c00