Fix a building issue

Summary:
Build regression introduced in D26847

https://build.neon.kde.org/job/bionic_unstable_kde_user-manager_bin_amd64/99/console

Test Plan: Builds

Reviewers: #plasma, ngraham, rikmills, jriddell

Reviewed By: jriddell

Subscribers: jriddell, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D26893