[Fix] Antivirus: use scanner-specific redis prefix
[Fix] Antivirus: use scanner-specific redis prefix

 - Reported by: @croessner

AlexeySa/rspamd,AlexeySa/rspamd,AlexeySa/rspamd,AlexeySa/rspamd,AlexeySa/rspamd,AlexeySa/rspamd,AlexeySa/rspamd,AlexeySa/rspamd,AlexeySa/rspamd