They can't void the policy unless it was a fraudulent statement, and they can't decline the claim if it is not related to the mistake/ incorrect statement in your proposal.
If it was related to the mistake, they might be able to reduce the amount paid, but otherwise they can't. You should let them know though, just in case you need to make a claim later that is related to the item in question. In some cases you may need to pay an additional premium (esp. if it relates to security features on the house).
Can discuss in more detail if you want to PM me.