net: dsa: mv88e6xxx: missing unlock on error path

We added a new error path, but we need to drop the lock before we return.

Fixes: 2d2e1dd2 ("net: dsa: mv88e6xxx: Cache the port cmode")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -2408,7 +2408,7 @@ static int mv88e6xxx_setup(struct dsa_switch *ds)
 		if (chip->info->ops->port_get_cmode) {
 			err = chip->info->ops->port_get_cmode(chip, i, &cmode);
 			if (err)
-				return err;
+				goto unlock;
 
 			chip->ports[i].cmode = cmode;
 		}