The node pointer returned by of_parse_phandle() with refcount incremented,
so add of_node_put() after using it in mtk_sgmii_init().

Fixes: 9ffee4a8 ("net: ethernet: mediatek: Extend SGMII related functions")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220428062543.64883-1-yangyingliang@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>