boards/cc2538dk: fix broken links
boards/cc2538dk: fix broken links

kaspar030/RIOT,ant9000/RIOT,kaspar030/RIOT,yogo1212/RIOT,jasonatran/RIOT,OlegHahm/RIOT,yogo1212/RIOT,ant9000/RIOT,ant9000/RIOT,basilfx/RIOT,RIOT-OS/RIOT,basilfx/RIOT,jasonatran/RIOT,kaspar030/RIOT,miri64/RIOT,yogo1212/RIOT,kYc0o/RIOT,miri64/RIOT,yogo1212/RIOT,yogo1212/RIOT,miri64/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,basilfx/RIOT,basilfx/RIOT,ant9000/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,kYc0o/RIOT,yogo1212/RIOT,ant9000/RIOT,authmillenon/RIOT,authmillenon/RIOT,miri64/RIOT,jasonatran/RIOT,OTAkeys/RIOT,kYc0o/RIOT,kaspar030/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,miri64/RIOT,jasonatran/RIOT,jasonatran/RIOT,kYc0o/RIOT,authmillenon/RIOT,basilfx/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,kaspar030/RIOT,OlegHahm/RIOT,authmillenon/RIOT,OlegHahm/RIOT