drivers/firmware/iscsi_ibft.c: use %pM to show MAC address

Use the %pM kernel extension to display the MAC address.

Also, remove the 'mac' variable and use nic->mac directly.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Peter Jones <pjones@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>