net: dsa: remove useless argument in legacy setup

dsa_switch_alloc() already assigns ds-dev, which can be used in
dsa_switch_setup_one and dsa_cpu_dsa_setups instead of requiring an
additional struct device argument.

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