net: dsa: remove dsa_port_phylink_validate()

As all drivers now provide phylink capabilities (including MAC), the
if() condition in dsa_port_phylink_validate() will always be true. We
will always use the generic validator, which phylink will call itself
if the .validate method isn't populated. Thus, there is now no need to
implement the .validate method, so this implementation can be removed.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>