drivers/enc28j60: fix typo 'Preamle' -> 'Preamble'
drivers/enc28j60: fix typo 'Preamle' -> 'Preamble'

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