tools/pydfu.py: Use getfullargspec instead of getargspec for newer pyusb
tools/pydfu.py: Use getfullargspec instead of getargspec for newer pyusb

pyusb v1.0.2 warns about `getargspec` as being deprecated.

adafruit/circuitpython,pramasoul/micropython,henriknelson/micropython,henriknelson/micropython,kerneltask/micropython,selste/micropython,adafruit/circuitpython,pozetroninc/micropython,henriknelson/micropython,kerneltask/micropython,pfalcon/micropython,kerneltask/micropython,bvernoux/micropython,pramasoul/micropython,bvernoux/micropython,MrSurly/micropython,pramasoul/micropython,pramasoul/micropython,kerneltask/micropython,tobbad/micropython,henriknelson/micropython,bvernoux/micropython,trezor/micropython,selste/micropython,selste/micropython,adafruit/circuitpython,pfalcon/micropython,MrSurly/micropython,pfalcon/micropython,kerneltask/micropython,trezor/micropython,adafruit/circuitpython,selste/micropython,tobbad/micropython,bvernoux/micropython,MrSurly/micropython,pfalcon/micropython,MrSurly/micropython,trezor/micropython,tobbad/micropython,trezor/micropython,pfalcon/micropython,pozetroninc/micropython,MrSurly/micropython,henriknelson/micropython,pozetroninc/micropython,tobbad/micropython,adafruit/circuitpython,pozetroninc/micropython,tobbad/micropython,adafruit/circuitpython,bvernoux/micropython,pozetroninc/micropython,trezor/micropython,pramasoul/micropython,selste/micropython