[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