fw2/Makefile: use the ATmega32U2 configuration (experimental) of avrdude
fw2/Makefile: use the ATmega32U2 configuration (experimental) of avrdude

- Makefile (prog): use $(CHIP) instead of $(CHIP_AVRDUDE)
- Makefile (CHIP_AVRDUDE): removed

cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan,cfriedt/ben-wpan