When configured in fixed link, the DaVinci emac driver sets the
priv->phydev to NULL and further ioctl calls to the phy_mii_ioctl()
causes the kernel to crash.

Cc: Brian Hutchinson <b.hutchman@gmail.com>
Fixes: 1bb6aa56 ("net: davinci_emac: Add support for fixed-link PHY")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>