ports: litex: use dfu.py instead of dfu-suffix.py
ports: litex: use dfu.py instead of dfu-suffix.py

dfu.py now generates proper dfu suffixes without the nonstandard prefix.

Signed-off-by: Sean Cross <d7e19930cc1f42c2d0781f4d9e6f1fe5891bf9cf@xobs.io>

adafruit/micropython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/micropython,adafruit/micropython,adafruit/circuitpython