pch_gbe: minor: report the actual error on MTU change

If we can't _up() after changing the MTU, report the actual error instead
of -ENOMEM. It can be really misleading cause pch_gbe is usually used in
scenarios where the memory amount is really small, and thus hiding the
real cause.
Signed-off-by: NVeaceslav Falico <vfalico@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c

@@ -2263,7 +2263,7 @@ static int pch_gbe_change_mtu(struct net_device *netdev, int new_mtu)
 		if (err) {
 			adapter->rx_buffer_len = old_rx_buffer_len;
 			pch_gbe_up(adapter);
-			return -ENOMEM;
+			return err;
 		} else {
 			netdev->mtu = new_mtu;
 			adapter->hw.mac.max_frame_size = max_frame;