More safe EEPROM access

Disable and re-enable interrupts during eeprom access.
The EEPROM doesn't like it at all if it gets interrupted.

From avr/eeprom.h:

    - As these functions modify IO registers, they are known to be
    non-reentrant.  If any of these functions are used from both,
    standard and interrupt context, the applications must ensure
    proper protection (e.g. by disabling interrupts before accessing
    them).