mlxsw: spectrum: Make unlinking functions return void

When responding to unlinking CHANGEUPPER notifications we shouldn't
return any value, as it's not checked by upper layers.

In addition, there's nothing the driver can do in case of failure, so it
should simply continue and try to free as much resources as possible and
not stop on first error.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>