ftdi_4222: Cleanup warning messages from compile
ftdi_4222: Cleanup warning messages from compile

    * Fixed broken switch statement - missing 'case' in front of labels
    * Added default case to switch statement
    * Removed unused variable
    * Removed unused static functions
    * Attempted to fix cases where functions are returning/not returning
      data incorrectly.
    * Attempted to fix i2c read which was returning an
    * uninitialized/unused variable.

Signed-off-by: Noel Eck <1e36ab6ededef40f3f16bdbc1b09eee72c5d08cf@intel.com>

KurtE/mraa,g-vidal/mraa,intel-iot-devkit/mraa,intel-iot-devkit/mraa,intel-iot-devkit/mraa,yongli3/mraa,stefan-andritoiu/mraa,stefan-andritoiu/mraa,Propanu/mraa,yongli3/mraa,stefan-andritoiu/mraa,arfoll/mraa,yongli3/mraa,arfoll/mraa,stefan-andritoiu/mraa,KurtE/mraa,Propanu/mraa,arfoll/mraa,stefan-andritoiu/mraa,KurtE/mraa,KurtE/mraa,Propanu/mraa,g-vidal/mraa,Propanu/mraa,arfoll/mraa,yongli3/mraa,g-vidal/mraa,Propanu/mraa,intel-iot-devkit/mraa,KurtE/mraa,g-vidal/mraa,intel-iot-devkit/mraa,g-vidal/mraa,yongli3/mraa,arfoll/mraa