net: ethernet: mtk_eth_soc: fix error handling in mtk_open()

[ Upstream commit f7007414 ]

If mtk_start_dma() fails, invoke phylink_disconnect_phy() to perform
cleanup. phylink_disconnect_phy() contains the put_device action. If
phylink_disconnect_phy is not performed, the Kref of netdev will leak.

Fixes: b8fc9f30

 ("net: ethernet: mediatek: Add basic PHYLINK support")
Signed-off-by: Liu Jian <liujian56@huawei.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20221117111356.161547-1-liujian56@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>