[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