Fix force font DPI UI logic
Summary:
The kcm UI has right now a step size of 24 with a max size of 1000 and a minimum of 1.
Max size need to divide to step size and the lowest possible value should be the step size
because 0 means disabled.
Reviewers: davidedmundson, Plasma
Reviewed By: davidedmundson, Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D25004