In case you have a trouble for updating the tap, perform uninstalling of the related tools and osx-cross/avr
tap:
brew remove avr-binutils avr-gcc
brew untap osx-cross/avr
For installing the tap, do the following:
brew tap osx-cross/avr
brew install avr-gcc
# avrdude is under homebrew-core
brew install avrdude
Note well: fuse bit definition between ATmega168 and ATmega328p are different from each other!