I didn't find a configuration setting within ClamAV itself, but I did find a script I could configure with cron (and an article that explains it):
# written by Tomas Nevar (firstname.lastname@example.org)
# 17/01/2014 (dd/mm/yy)
# copyleft free software
The e0 command is STANDBY IMMEDIATE. I think that is being sent by power management to put the drive to sleep after a period of inactivity. Turning that off should get rid of the cause of the error, rather than just mask the logging.
The "Winston kernel:" string is not part of the msg property, which usually begins with the space after the ":".
The regex operation uses Posix BRE (basic regular expressions), so \d does not exist; instead try [0-9]. Also, + does not exist, and you will need *. Alternatively, if supported, you can use the extended regex operation: ereregex; you will ...
The link(s) between journald and rsyslog is controlled on the rsyslog side through the use of its input and output modules; there is an imjournal and omjournal for reading from and writing to the journal respectively.
So if you write something to rsyslog, it will only appear in journald if you've configured the omjournal module.
rsyslog "owns" /var/log/...