libusb1: Fix get_extra on python 2.7 .
libusb1: Fix get_extra on python 2.7 .

Whereas single-item retrieval on a "bytes" instance yields a string and
hence requires an "ord" call, on "bytearray" instance it yields an integer
directly. This was broken by:
  commit b26f6cdbdb269ccf4d57965387071b21545cb912
  Author: Vincent Pelletier <plr.vincent@gmail.com>
  Date:   Sun Oct 16 11:14:04 2016 +0000

      Use writeable buffer for transfers (sync & async).
along with buffer_at cast to bytearray.

vpelletier/python-libusb1,vpelletier/python-libusb1