cpu/nrf52: update RIOTBOOT_LEN w/ MODULE_USBUS_DFU
cpu/nrf52: update RIOTBOOT_LEN w/ MODULE_USBUS_DFU

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