fs_enet: Revive fixed link support

Since commit aa73832c

 ("Rework
fs_enet driver to use of_mdio infrastructure") the fixed-link support
is broken in the fs_enet driver.

This patch fixes the support by removing a check for phy_node, and adding
a call to of_phy_connect_fixed_link().

Also set netdev parent device via SET_NETDEV_DEV() call, this is needed
so that OF MDIO core could find a node pointer for a device.

Plus, fix "if (IS_ERR(phydev))" check, in case of errors,
of_phy_connect() returns NULL, not ERR_PTR as phy_connect().

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>