Fix multiline comment

Author: scottwulf

chef/cookbooks/ceph/recipes/mon.rb

@@ -88,6 +88,7 @@
       add_key.error!
 
       # no need to check if the attribute is already set: it's part of the
+      # only_if
       node.set["ceph"]["monitor-secret"] = monitor_key
       node.save
     end