The "priv->phy_mode" variable is an enum and in this context GCC will
treat it as unsigned to the error handling will never trigger.

Fixes: 57c5bc9a ("net: hisilicon: add hix5hd2 mac driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>