[kicker] Fix a few unqualified property access

Summary: Those will break in Qt 6. Port a few trivial ones suggested by qmllint

Test Plan: Did kicker and dashboard things

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: davidedmundson, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D26224