au1000_eth: use eth_hw_addr_random() instead of random_ether_addr()

Use eth_hw_addr_random() instead of calling random_ether_addr()
to set addr_assign_type correctly to NET_ADDR_RANDOM.

v2: adapt to eth_hw_addr_random()

Signed-off-by: Danny Kukawka <danny.kukawka@bisect.de>
Signed-off-by: David S. Miller <davem@davemloft.net>