net: dsa: fix spurious error message when unoffloaded port leaves bridge

Flip the sign of a return value check, thereby suppressing the following
spurious error:

  port 2 failed to notify DSA_NOTIFIER_BRIDGE_LEAVE: -EOPNOTSUPP

... which is emitted when removing an unoffloaded DSA switch port from a
bridge.

Fixes: d371b7c9 ("net: dsa: Unset vlan_filtering when ports leave the bridge")
Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20211012112730.3429157-1-alvin@pqrs.dkSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/switch.c

@@ -168,7 +168,7 @@ static int dsa_switch_bridge_leave(struct dsa_switch *ds,
 		if (extack._msg)
 			dev_err(ds->dev, "port %d: %s\n", info->port,
 				extack._msg);
-		if (err && err != EOPNOTSUPP)
+		if (err && err != -EOPNOTSUPP)
 			return err;
 	}