Litchfield, Cavo LLP is growing again, and its spurning a trend toward open-floor design and single-sized offices for all lawyers.The litigation defense firm that opened in Chicago in 1998 with 12 lawyers now has 55 in town and has agreed to expand its lease at 303 W. Madison St. by nearly 5,000 square feet.This is at least the fifth such expansion for the firm’s Chicago office, which will now occupy nearly 40,000 square feet on floors two through five.The firm took up 3 percent of the building’s space when it …