tests/driver_pca9633: fix conflict with libc function name
tests/driver_pca9633: fix conflict with libc function name

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