net: dsa: slave: Remove MDIO address from switch MDIO bus name

The DSA layer should no longer assume the switch is connected to an
MDIO bus. As a result, we cannot use the address on the MDIO bus when
forming the name of the switches internal MDIO bus for its builtin and
possibly external PHYs. The switch index is sufficient to make the
name unique, so drop the MDIO address.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>