cmd_eeprom: fix i2c_{read|write} usage if env is in I2C EEPROM

Data "offset" is not used directly in case of I2C EEPROM. Istead it is
split into "block number" and "offset within mentioned block". Which are
"addr[0]" and "addr[1]" respectively.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
cc: Peter Tyser <ptyser@xes-inc.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: Mischa Jonker <mjonker@synopsys.com>