ath9k_hw: restore mac address reading logic

Once upon a time the AR_EEPROM_MAC macro was added to let us
add a random attribute to the three 4-bytes of MAC addresses
entries we read from the EEPROM. This was good while a random
high-enough value was used which did not conflict with any
of the already existing enum eeprom_param values. With AR9003
support the enums overlap and it means we either increment
the random offset or just restore the reading logic to match
what the HAL has. I choose to do the later to synchronize
the logic on both code bases.

This should fix reading the MAC address from the EEPROM
on AR9003 hardware.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>