stm32/usb: Fix broken pyb.have_cdc() so it works again.
stm32/usb: Fix broken pyb.have_cdc() so it works again.

swegener/micropython,pfalcon/micropython,ryannathans/micropython,tobbad/micropython,MrSurly/micropython,trezor/micropython,pramasoul/micropython,tobbad/micropython,pramasoul/micropython,adafruit/micropython,ryannathans/micropython,adafruit/micropython,adafruit/micropython,MrSurly/micropython,dmazzella/micropython,kerneltask/micropython,kerneltask/micropython,kerneltask/micropython,adafruit/circuitpython,pfalcon/micropython,bvernoux/micropython,kerneltask/micropython,pramasoul/micropython,swegener/micropython,trezor/micropython,ryannathans/micropython,tralamazza/micropython,adafruit/circuitpython,selste/micropython,selste/micropython,ryannathans/micropython,tobbad/micropython,tobbad/micropython,kerneltask/micropython,tralamazza/micropython,bvernoux/micropython,swegener/micropython,henriknelson/micropython,henriknelson/micropython,henriknelson/micropython,pozetroninc/micropython,selste/micropython,pfalcon/micropython,adafruit/circuitpython,bvernoux/micropython,selste/micropython,ryannathans/micropython,dmazzella/micropython,tralamazza/micropython,adafruit/circuitpython,trezor/micropython,swegener/micropython,trezor/micropython,henriknelson/micropython,selste/micropython,MrSurly/micropython,bvernoux/micropython,pozetroninc/micropython,MrSurly/micropython,swegener/micropython,pozetroninc/micropython,pramasoul/micropython,henriknelson/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/micropython,adafruit/circuitpython,tralamazza/micropython,MrSurly/micropython,tobbad/micropython,trezor/micropython,bvernoux/micropython,pramasoul/micropython,dmazzella/micropython,pfalcon/micropython,pfalcon/micropython,pozetroninc/micropython,dmazzella/micropython,pozetroninc/micropython