net: dsa: unregister cross-chip notifier after ds->ops->teardown

net: dsa: unregister cross-chip notifier after ds->ops->teardown

To be symmetric with the error unwind path of dsa_switch_setup(), call
dsa_switch_unregister_notifier() after ds->ops->teardown.

The implication is that ds->ops->teardown cannot emit cross-chip
notifiers. For example, currently the dsa_tag_8021q_unregister() call
from sja1105_teardown() does not propagate to the entire tree due to
this reason. However I cannot find an actual issue caused by this,
observed using code inspection.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20211012123735.2545742-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>