Mar. 12—As the misses kept piling up and the paint kept chipping off the iron at both ends of the AT&T Center, it soon became clear Sunday’s tilt between the Spurs and Oklahoma City was not shaping up to be a masterclass in offensive basketball. “It wasn’t a great offensive show by either team,” Spurs coach Gregg Popovich said. It is an immutable rule of the NBA, however, that one team has…