Fixes wrong parameter name.

resources/prosody-plugins/mod_muc_poltergeist.lua

 
     local room = get_room(room_name, group);
     if (not room) then
-        log("error", "no room found %s", room_address);
+        log("error", "no room found %s", room_name);
         return 404;
     end
 
 
     local room = get_room(room_name, group);
     if (not room) then
-        log("error", "no room found %s", room_address);
+        log("error", "no room found %s", room_name);
         return 404;
     end