Mallinckrodt plc has completed its planned acquisition of Cadence Pharmaceuticals, a $1.4 billion deal the company has said will strengthen its specialty drug business. In February, Mallinckrodt announced an agreement to acquire San Diego, Calif.,-based Cadence for $14 a share, or about $1.3 billion. Mallinckrodt officials said Wednesday that the deal was valued at $1.4 billion at closing. The deal will add an intravenous pain killer, Ofirmev, to Mallinckrodt’s portfolio, which Mallinckrodt CEO…