net: phylink: Remove redundant netdev.phydev assignment

As a part of working on MII time stamping infrastructure, I was trying
to figure out how netdev->phydev gets assigned, and I stumbled across
this.  Ever since the new phylink code came in, the field is assigned
twice.

The function, phylink_connect_phy(), calls

	phy_attach_direct()
	phylink_bringup_phy()

and phy_attach_direct() sets

	dev->phydev = phydev;

but phylink_bringup_phy() then sets the same field again:

	pl->netdev->phydev = phy;

Similarly, the function, phylink_of_phy_connect(), calls

	of_phy_attach()
		phy_attach_direct()
	phylink_bringup_phy()

The removal code is also duplicated:

phylink_disconnect_phy()
	pl->netdev->phydev = NULL;
	phy_disconnect()
		phy_detach()
			phydev->attached_dev->phydev = NULL;

This patch removes the redundant assignments, restricting manipulation
of the netdev.phydev field to phy_attach_direct() and phy_detach().

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>