net: dsa: sja1105: call dsa_unregister_switch when allocating memory fails

Unlike other drivers which pretty much end their .probe() execution with
dsa_register_switch(), the sja1105 does some extra stuff. When that
fails with -ENOMEM, the driver is quick to return that, forgetting to
call dsa_unregister_switch(). Not critical, but a bug nonetheless.

Fixes: 4d752508 ("net: dsa: sja1105: offload the Credit-Based Shaper qdisc")
Fixes: a68578c2

 ("net: dsa: Make deferred_xmit private to sja1105")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>