pkg/libcose: fixup backend ducomentation
pkg/libcose: fixup backend ducomentation

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