docs/logging: corrected example register() syntax
docs/logging: corrected example register() syntax

sentinelleader/qpsmtpd-dev,priyadi/qpsmtpd,salvis/qpsmtpd,smtpd/qpsmtpd,priyadi/qpsmtpd,priyadi/qpsmtpd,smtpd/qpsmtpd,salvis/qpsmtpd,sieutruc/qpsmtpd,msimerson/qpsmtpd,sieutruc/qpsmtpd,sentinelleader/qpsmtpd-dev,sieutruc/qpsmtpd,msimerson/qpsmtpd