net: hns3: Fixes the wrong IS_ERR check on the returned phydev value

This patch removes the wrong check being done for the phy device being
returned by the mdiobus_get_phy() function. This function never returns
the error pointers.

Fixes: 256727da ("net: hns3: Add MDIO support to HNS3 Ethernet
Driver for hip08 SoC")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>