I'm not sure how this would/could work unless you've been green lighted for assisted suicide. Even then, I'm not sure whether you can donate organs to a specific person you are in contact with. I imagine more- they remove the organs and they go to whoever is compatible and needs them most.
If it's a DIY suicide though- I imagine the organs need to be harvested within a (sometimes fairly narrow I think) time period. That means either you or your recipient family notifying medical personal as soon as possible after you've died. They may arrive too early- in which case- they will try to save you. If the recipient family contact them and say you promised them your kidney after you'd killed yourself- I imagine they would be in legal trouble. Maybe it's not assisting a suicide as such but it's letting it happen for personal gain.
Plus again, I doubt it works like that. I expect it has to be done via official medical channels and I doubt any would accept someone saying- take my organs after I've killed myself and give them to this specific person.
Like others have said- the method of suicide I would think may also damage the organs in some cases. Again- this could be done if assisted suicide was legalised, regulated and performed in clinics. I expect a lot of us would feel happier if we knew we were helping someone who actually wanted to live. It seems such a waste really.