net: aquantia: add an error handling in aq_nic_set_multicast_list

add an error handling in aq_nic_set_multicast_list, it may not
work when hw_multicast_list_set error; and at the same time
it will remove gcc Wunused-but-set-variable warning.
Signed-off-by: Chenwandun <chenwandun@huawei.com>
Reviewed-by: Igor Russkikh <igor.russkikh@aquantia.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/aquantia/atlantic/aq_nic.c

@@ -664,6 +664,8 @@ int aq_nic_set_multicast_list(struct aq_nic_s *self, struct net_device *ndev)
 		err = hw_ops->hw_multicast_list_set(self->aq_hw,
 						    self->mc_list.ar,
 						    self->mc_list.count);
+		if (err < 0)
+			return err;
 	}
 	return aq_nic_set_packet_filter(self, packet_filter);
 }