Fix bad button construction in Owners

Summary: Fixes T7618. The "button" needs to be a PHUIButtonView later on.

Test Plan: Forced condition, loaded page, saw button instead of fatal.

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7618

Differential Revision: https://secure.phabricator.com/D12108