[wayland] Fix arguments to clientMaximizedStateChanged(bool, bool)

Summary:
It should be indicating the current state of horizontal and vertical
maximisation not whether it changed or not.

Reviewers: #kwin, zzag

Reviewed By: #kwin, zzag

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D16740