cxgb4: support eeprom read/write on functions other than 0

Extend the address translation for eeprom read/write (code used by
ethtool -[eE]) to functions other than 0.

Signed-off-by: Dimitris Michailidis <dm@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>