net: dsa: remove dev arg of dsa_register_switch

The current dsa_register_switch function takes a useless struct device
pointer argument, which always equals ds->dev.

Drivers either call it with ds->dev, or with the same device pointer
passed to dsa_switch_alloc, which ends up being assigned to ds->dev.

This patch removes the second argument of the dsa_register_switch and
_dsa_register_switch functions.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>