parts: fix i2c_eeprom addressing

Fixes the following issues:

> I2C eeprom address and address mask not set during init. This
  caused a device at any address on the bus to be recognised.
> For the address mask to behave as per the comment in
  i2c_eeprom.h it needed inverting.
twi: Clear TWSTO bit in the TWCR register after STOP condition transmitted

Referenced in for example p188 of the ATMega32A datasheet
(rev 815D-AVR-10/2013).