A smartphone with a displayed Arm Ltd logo is placed on a computer motherboard in this illustration taken March 6, 2023. REUTERS/Dado Ruvic/Illustration/File Photo/File Photo Acquire Licensing Rights NEW YORK, Sept 13 (Reuters) - Chip designer Arm Holdings Plc (ARM.O) secured a $54.5 billion valuation in its U.S. initial public offering (IPO) on Wednesday, seven years after its owner SoftBank Group Corp (9984.T) took the company private for $32 billion. The IPO represents a climb-down from the $64 billion valuation at which SoftBank last month acquired the 25% stake it did not already own in the company from the $100...