drivers/dose: fix declaration of signal()
drivers/dose: fix declaration of signal()

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