drivers/at25xxx: Fix kconfig model
drivers/at25xxx: Fix kconfig model

miri64/RIOT,miri64/RIOT,miri64/RIOT,kaspar030/RIOT,kaspar030/RIOT,kaspar030/RIOT,kYc0o/RIOT,kaspar030/RIOT,jasonatran/RIOT,ant9000/RIOT,kYc0o/RIOT,ant9000/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,miri64/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,kYc0o/RIOT,jasonatran/RIOT,miri64/RIOT,kYc0o/RIOT,ant9000/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,ant9000/RIOT,jasonatran/RIOT,ant9000/RIOT,jasonatran/RIOT,RIOT-OS/RIOT