olpc_battery: Fix up eeprom read function

The eeprom read function was placing values into the wrong place in
'buf'; we were starting from buf[off], rather than buf[0].

Also, the for loop that we were using was much uglier than it needed to
be.  This cleans it up a bit.

Signed-off-by: Andres Salomon <dilinger@collabora.co.uk>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>