Correct _PDO_RESPONSE_CODES list

According to the HUSB238 datasheet the value 010 in the PD_RESPONSE section of
the PD_STATUS1 register should be reserved.

Updated the _PDO_RESPONSE_CODES list to account for this, so that when the list
is accessed using the self.response value the correct response string is
returned.

Author: MattHoward-GH

adafruit_husb238.py

@@ -143,6 +143,7 @@ class Adafruit_HUSB238:
     _PDO_RESPONSE_CODES = [
         "NO RESPONSE",
         None,  # Success
+        None,  # Reserved
         "INVALID COMMAND OR ARGUMENT",
         "COMMAND NOT SUPPORTED",
         "TRANSACTION FAILED, NO GOOD CRC",