dpaa_eth: remove netdev_err() for user errors

User reports that an application making an (incorrect) call to
restart AN on a fixed link DPAA interface triggers an error in
the kernel log while the returned EINVAL should be enough.

Reported-by: Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
Signed-off-by: Madalin Bucur <madalin.bucur@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>