net: dsa: mv88e6xxx: drop adjust_link to enabled phylink

We have to drop the adjust_link callback in order to finally migrate to
phylink.

Otherwise we get the following warning during startup:
  "mv88e6xxx 2188000.ethernet-1:10: Using legacy PHYLIB callbacks. Please
   migrate to PHYLINK!"

The warning is generated in the function dsa_port_link_register_of in
dsa/port.c:

  int dsa_port_link_register_of(struct dsa_port *dp)
  {
  	struct dsa_switch *ds = dp->ds;

  	if (!ds->ops->adjust_link)
  		return dsa_port_phylink_register(dp);

  	dev_warn(ds->dev,
  		 "Using legacy PHYLIB callbacks. Please migrate to PHYLINK!\n");
  	[...]
  }

Signed-off-by: Hubert Feurstein <h.feurstein@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>