net: ethernet: mtk_eth_wed: add missing put_device() in mtk_wed_add_hw()

After calling get_device() in mtk_wed_add_hw(), in error path, put_device()
needs be called.

Fixes: 804775df ("net: ethernet: mtk_eth_soc: add support for Wireless Ethernet Dispatch (WED)")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>