net: nixge: fix potential memory leak in nixge_probe()

If some processes in nixge_probe() fail, free_netdev(dev)
needs to be called to aviod a memory leak.

Fixes: 87ab2079 ("net: nixge: Separate ctrl and dma resources")
Fixes: abcd3d6f

 ("net: nixge: Fix error path for obtaining mac address")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Lu Wei <luwei32@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>