bna: fill the magic in bnad_get_eeprom() instead of validating

A driver should fill magic field of ethtool_eeprom struct in .get_eeprom
and validate it in .set_eeprom. The bna incorrectly validates it in both
and this makes its .get_eeprom interface unusable.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>