Add of_node_put() if of_get_phy_mode() fails in mt7530_setup()

Fixes: 0c65b2b9 ("net: of_get_phy_mode: Change API to solve int/unit warnings")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220428095317.538829-1-yangyingliang@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>