cmd_eeprom: bug fix for i2c read/write

cmd_eeprom: bug fix for i2c read/write

The local pointer of address (i.e., addr) only gets
referenced under SPI mode, and it won't be appropriate
to pass only 1-byte addr[1] to i2c_read/i2c_write while
CONFIG_SYS_I2C_EEPROM_ADDR_LEN > 1.

1. In U-boot's I2C model, the address would be re-assembled
   to a byte string in MSB order inside I2C controller drivers.

2. The 'CONFIG_SYS_I2C_EEPROM_ADDR_OVERFLOW' option which could
   be found at soft_i2c.c is always turned on in cmd_eeprom.c,
   the addr[0] always contains the device address with overflowed
   MSB address bits.

Signed-off-by: Kuo-Jung Su <[email protected]>
Cc: Alexey Brodkin <[email protected]>
Cc: Jean-Christophe PLAGNIOL-VILLARD <[email protected]>
cc: Peter Tyser <[email protected]>
Cc: Heiko Schocher <[email protected]>
Cc: Wolfgang Denk <[email protected]>
Cc: Stefan Roese <[email protected]>
Cc: Mischa Jonker <[email protected]>