conf: fix logic error for scsi units

Introduced in c8007fdc, it should use 'greater than max' instead of
'equal or greater than max' for the condition of checking invalid scsi
unit.
Signed-off-by: NHan Han <hhan@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

src/conf/domain_conf.c

@@ -4850,7 +4850,7 @@ virDomainSCSIDriveAddressIsUsed(const virDomainDef *def,
             break;
         }
 
-        if (max != -1 && addr->unit >= max)
+        if (max != -1 && addr->unit > max)
             return true;
         if (reserved != -1 && addr->unit == reserved)
             return true;