net: dsa: mv88e6xxx: Take switch out of reset before probe

The switch needs to be taken out of reset before we can read its ID
register on the MDIO bus.

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