net: ethernet: remove redundant null pointer check before of_node_put

of_node_put has taken the null pointer check into account. So it is
safe to remove the duplicated check before of_node_put.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Reviewed-by: Vladimir Zapolskiy <vz@mleia.com>
Acked-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>