Use correct method name in Harbormaster UI event listener

Summary: See thread; fixes fatal. The actual name of this method is `getHarbormaster...`.

NOTE: This fixes a fatal in Differential which impedes review, so I'm pushing it as-is.

Test Plan: Browsed a revision.

Reviewers: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7834