fix logic of lnf loading

Summary:
mDefaultLnfConfig must be breeze, and mLnfConfig should be the
configured one, rather the other way around

Test Plan: plasma seems to start with proper icons now

Reviewers: #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D18260