[pfff] make token exist for enum values

Summary:
The prolog db really needs a token in that particular location, so
use the semicolon's token when there isn't one in the actual code.

Test Plan: Omitted.

Reviewers: pad, mareksapota

Reviewed By: mareksapota

Subscribers: mareksapota, dominik

Differential Revision: https://phabricator.fb.com/D1592391

Tasks: 5251128