Quickly fix phpqrcode syntax
Summary: phpqrcode has some old looking php syntax. Fix it quickly since it's one line.
Before this patch, went to add a TOTP token, saw the error about the undefined variable.
After this patch, successfully added a TOTP token, and used it.
Reviewers: avivey, epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Maniphest Tasks: T9300
Differential Revision: https://secure.phabricator.com/D14019