Fix variable mixup

Summary:
Caused icons to be not longer recolored when changing the color scheme until an
application is started again

Test Plan: Change color scheme while having an application open, icons should change color correctly

Reviewers: Breeze, Plasma, ndavis

Reviewed By: Breeze, ndavis

Subscribers: ndavis, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D29012