net: stmmac: dwmac-sun8i: add missing of_node_put() in sun8i_dwmac_register_mdio_mux()

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

Fixes: 634db83b ("net: stmmac: dwmac-sun8i: Handle integrated/external MDIOs")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220428095716.540452-1-yangyingliang@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c

@@ -907,6 +907,7 @@ static int sun8i_dwmac_register_mdio_mux(struct stmmac_priv *priv)
 
 	ret = mdio_mux_init(priv->device, mdio_mux, mdio_mux_syscon_switch_fn,
 			    &gmac->mux_handle, priv, priv->mii);
+	of_node_put(mdio_mux);
 	return ret;
 }