net: phy: Check harder for errors in get_phy_id()

Commit 02a6efca ("net: phy: allow scanning busses with missing
phys") added a special condition to return -ENODEV in case -ENODEV or
-EIO was returned from the first read of the MII_PHYSID1 register.

In case the MDIO bus data line pull-up is not strong enough, the MDIO
bus controller will not flag this as a read error. This can happen when
a pluggable daughter card is not connected and weak internal pull-ups
are used (since that is the only option, otherwise the pins are
floating).

The second read of MII_PHYSID2 will be correctly flagged an error
though, but now we will return -EIO which will be treated as a hard
error, thus preventing MDIO bus scanning loops to continue succesfully.

Apply the same logic to both register reads, thus allowing the scanning
logic to proceed.

Fixes: 02a6efca ("net: phy: allow scanning busses with missing phys")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>