[kstyle] Fix deprecation warnings
Summary: See https://build.kde.org/job/Plasma%20breeze%20kf5-qt5%20FreeBSDQt5.11/4/warnings12Result/
Test Plan: Compiles.
Reviewers: Plasma, broulik
Reviewed By: Plasma, broulik
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D15285