add description for update 6200

Small cosmetic annoyance:

anarcat@ceres:/var/aegir/clients/anarcat/anarcat.koumbit.org$ drush updatedb
The following updates are pending:

 honeypot module
 6100 - Update Honeypot user registration form variable.
 6200 - description not available

Just adding a comment on top of honeypot_update_6200() should be enough to fix this.