tests/embunit: fix NDEBUG compile problem
tests/embunit: fix NDEBUG compile problem

ant9000/RIOT,yogo1212/RIOT,OlegHahm/RIOT,basilfx/RIOT,OTAkeys/RIOT,yogo1212/RIOT,basilfx/RIOT,jasonatran/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,miri64/RIOT,kaspar030/RIOT,kYc0o/RIOT,yogo1212/RIOT,OTAkeys/RIOT,miri64/RIOT,kaspar030/RIOT,yogo1212/RIOT,ant9000/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,kYc0o/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kYc0o/RIOT,miri64/RIOT,jasonatran/RIOT,OTAkeys/RIOT,ant9000/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,basilfx/RIOT,kYc0o/RIOT,miri64/RIOT,authmillenon/RIOT,authmillenon/RIOT,basilfx/RIOT,kaspar030/RIOT,authmillenon/RIOT,basilfx/RIOT,OlegHahm/RIOT,miri64/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,yogo1212/RIOT,yogo1212/RIOT,kaspar030/RIOT,ant9000/RIOT,OlegHahm/RIOT,ant9000/RIOT,authmillenon/RIOT,authmillenon/RIOT