sys/suit: make use of riotboot_slot_offset()
sys/suit: make use of riotboot_slot_offset()

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