pkg/pkg.mk: silent prepare target when there's nothing to be done
pkg/pkg.mk: silent prepare target when there's nothing to be done

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