Dr. Benjamin S. Carson, renowned chief of pediatric neurosurgery at Johns Hopkins Hospital, underwent a two-hour operation at Hopkins yesterday for prostate cancer and should be ready to go home by Saturday, his surgeon said. Although tests indicating whether the cancer had spread will take a few days to complete, Dr. Patrick Walsh said, the disease appeared confined to the prostate gland. If lab studies confirm that, he said, the possibility for a cure will be high. "Everything looked good," said Walsh, Hopkins' chief of urology. "I've said I think this is a curable cancer, and everything today looked compatible...