dm9000 EEPROM reading bugfix

Make the U-Boot dm9000 driver read addresses from EEPROM just
like Linux does ... read six bytes, instead of reading twelve
bytes and then discarding every other one.

Using the right Ethernet address is a big win.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Ben Warren <biggerbadderben@gmail.com>