Fix has_constant_parameter_count() confusion in LReturn

BUG=chromium:431602
LOG=y
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/714663002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25249 ce2b1a6d-e550-0410-aec6-3dcde31c8c00