Fix config read for AVR devices with one or two fuses

Not all families have three. Not sure if there's better way to derermine,
but seems like protocol variant is a pretty safe, though a bit ugly, way
to determine the family. Manually checked against the vendor utility's GUI.

Tested with ATMEGA32, should fix the issue #23 too.
Merge pull request #25 from lkundrak/lr-atmega32

Fix config read for AVR devices with one or two fuses