sys/random: Fix typo in kconfig
sys/random: Fix typo in kconfig

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