igb: Fix NULL assignment to incorrect variable in igb_reset_q_vector

adapter->tx_ring is set to NULL where rx_ring should be.

Fixes: 5536d210 ("igb: Combine q_vector and ring allocation into a single function")
Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -1036,7 +1036,7 @@ static void igb_reset_q_vector(struct igb_adapter *adapter, int v_idx)
 		adapter->tx_ring[q_vector->tx.ring->queue_index] = NULL;
 
 	if (q_vector->rx.ring)
-		adapter->tx_ring[q_vector->rx.ring->queue_index] = NULL;
+		adapter->rx_ring[q_vector->rx.ring->queue_index] = NULL;
 
 	netif_napi_del(&q_vector->napi);