pkg/tinydtls: fix detection of Kconfig usage
pkg/tinydtls: fix detection of Kconfig usage

kaspar030/RIOT,ant9000/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,kYc0o/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,jasonatran/RIOT,kaspar030/RIOT,kYc0o/RIOT,ant9000/RIOT,OlegHahm/RIOT,ant9000/RIOT,kYc0o/RIOT,miri64/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,miri64/RIOT,kaspar030/RIOT,OlegHahm/RIOT,jasonatran/RIOT,jasonatran/RIOT,miri64/RIOT,ant9000/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,miri64/RIOT,miri64/RIOT,ant9000/RIOT,jasonatran/RIOT,kaspar030/RIOT,jasonatran/RIOT