The survival of Louis II at Mohacs could do the trick. Even if the Hungarians are defeated there, he may be able to rally Hungarian troops and fight longer. Hungary might still lose its war agaisnt Sulleyman and the Turks, but remain independant despite loss of territory.
Not to mention Louis II's survival would prevent the dispute between Archduke Ferdinand (later Ferdinand I, Holy Roman Emperor and King of Hungary) and John Zápolya (a national hero and voïvode (later Grand Prince) of Transylvania) which led to the partition of Hungary between the Hapsburgs (who got Royal Hungary), Transylvania (who became a Turkish Protectorate) and the Ottomans (who conquered a bit of Hungary).
Another good POD could have John Zápolya take part in the battle of Mohacs : he was apparently leading an army for the battle, but never took part in it. Don't know if that would change things much, but who knows?