i2c: slave-eeprom: Add comment about address handling

The behaviour of the EEPROM in the case where we only send an 8bit
address to a 16bit address EEPROM is not defined. Added comment about
that the slave-eeprom might behave differently from how an actual device
does (only one model measured).

Reported-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Björn Ardö <bjorn.ardo@axis.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>