net: ftgmac100: add missing error return code in ftgmac100_probe()

The variables will be free on path err_phy_connect, it should
return error code, or it will cause double free when calling
ftgmac100_remove().

Fixes: bd466c3f ("net/faraday: Support NCSI mode")
Fixes: 39bfab88 ("net: ftgmac100: Add support for DT phy-handle property")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>