dsa:mv88e6xxx: allow address 0x1 in smi_init

Some devices, such as the mv88e6097 do have ADDR[0] external and so it
is possible to configure the device to use SMI address 0x1. Remove the
restriction, as there are boards using this address.

Signed-off-by: Volodymyr Bendiuga <volodymyr.bendiuga@westermo.se>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>