EAST POINT, Ga. -- A veteran detective calls it one of the dumbest mistakes he's ever seen. Now that mistake has put a suspected bank robber in jail.   East Point police said they easily arrested a robbery suspect because he had a cab pick him up and take him to the bank. Officers said they simply returned to the address and arrested him there.  "I've been a police officer for 18 years and this is one of the dumbest acts I've ever seen," said Capt. Russell Popham with the East Point Police Department.  Popham said he and other officers were able to pick up Marcus Chisholm at the Camp Creek Parkway apartment where he lived in large part because just an hour and 15 minutes earlier Chisholm had a cab pick him up at the same address and take him to a SunTrust Bank which, Popham said, Chisholm then robbed...