LAS VEGAS — Jon Jones could face a lengthy suspension from mixed martial arts after the UFC light heavyweight champion was notified Tuesday of his second potential violation of the promotion’s anti-doping policy. Jones is widely considered the top pound-for-pound fighter in his sport. The potential violation stems from a sample collected after his weigh-in July 28 for his title fight against Daniel Cormier at UFC 214 in Anaheim, California. Jones (23-1) beat Cormier with a vicious third-round head kick, reclaiming his 205-pound belt after sitting out the previous year under suspension for his first failed doping test.