s390/qeth: remove unused fallback in Layer3's MAC code

If the CREATE ADDR sent by qeth_l3_iqd_read_initial_mac() fails, its
callback sets a random MAC address on the net_device. The error then
propagates back, and qeth_l3_setup_netdev() bails out without
registering the net_device.

Any subsequent call to qeth_l3_setup_netdev() will then attempt a fresh
CREATE ADDR which either 1) also fails, or 2) sets a proper MAC address
on the net_device. Consequently, the net_device will never be registered
with a random MAC and we can drop the fallback code.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>