Prasanthi,
Module userroles are not available in the client (or in Studio Pro except when setting module security and defining app userrols), so I don't think you'll be able to use those to achieve this. You could create 2 separate app userroles or you could create another mechanism for controlling visibility / access to workflows outside of the userroles.
For instance, in one of our apps, we have created an approval level entity which controls which users are available as approvers and which users can see all approval workflows vs. workflows they are a performer for.
Hope that helps,
Mike