DynamicTablesPkg: SsdtSerialPortLibArm fix ECC error
    
    Fix the following ECC reported error in SsdtSerialPortLibArm.
      - [5007]  There should be no initialization of a variable as part of
                its declaration Variable Name.
    
    Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
    Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>