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

salvis/qpsmtpd,salvis/qpsmtpd,sieutruc/qpsmtpd,msimerson/qpsmtpd,smtpd/qpsmtpd,sieutruc/qpsmtpd,priyadi/qpsmtpd,priyadi/qpsmtpd,msimerson/qpsmtpd,priyadi/qpsmtpd,smtpd/qpsmtpd,sieutruc/qpsmtpd