net: fec: Issue error for missing but expected PHY

If the PHY is missing but expected, e.g. because of a typ0 in the dt
file, it is not possible to open the interface. ip link returns:

RTNETLINK answers: No such device

It is not very obvious what the problem is. Add a netdev_err() in this
case to make it easier to debug the issue.

[   21.409385] fec 2188000.ethernet eth0: Unable to connect to phy
RTNETLINK answers: No such device

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>