drivers/ethos: Fix off-by-one in ETHOS driver
drivers/ethos: Fix off-by-one in ETHOS driver

RIOT-OS/RIOT,ant9000/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,ant9000/RIOT,ant9000/RIOT,ant9000/RIOT