@Lew Zealand is correct, but I have a question: How'd it get up there???
If you throw something out of your inventory while next to a wall, without any magnet rings, it's possible for that to happen.
I've never seen it with the farmhouse (probably because I usually don't toss stuff out of my inventory while standing right next to the door). Where I've seen this a lot is that on Spring 5, one particular crate near the entrance to floor 2 of the mines has a chance of being a club, and it's possible to hit the crate wrong so the club gets stuck in the wall like that. It's also possible to toss your Rusty Sword out of your inventory wrong, so it gets stuck in the wall like that. When both these things happen it can be, er, "fun".
Hi espmy and Welcome to the Forums!
It will probably despawn by the next day or three as most things left out on the various maps are removed after a period of time (I don't remember the item culling period). As it's too early in your game to have a Magnet Ring, you probably won't be able to pick it up before it disappears.
Items that you dropped out of your inventory don't despawn until you exit the save file. So espmy, if you exit to title or close the game it should disappear. If you really want it back you have to keep the game open on that save file until you get a magnet ring. But I wouldn't bother, one clay isn't a huge deal.