macb: use random mac if stored address in EEPROM is invalid

We should use a random mac address if the EEPROM doesn't contain a valid
one. This makes life on Boards with unprogrammed EEPROM devices easier.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>