[platforms/hwcomposer] Make createOutput a non-static method

Summary:
there is no need for createOutput to be static, make it non-static,
this also fixes the build failure introduced in commit
02d3daf28a474d7d7a30af9afcd73e41fcd960f2.

Test Plan: builds

Reviewers: KWin, graesslin, davidedmundson

Reviewed By: davidedmundson

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D8430