sfc: farch: fix TX queue lookup in TX event handling

We're starting from a TXQ label, not a TXQ type, so
 efx_channel_get_tx_queue() is inappropriate (and could return NULL,
 leading to panics).

Fixes: 12804793 ("sfc: decouple TXQ type from label")
Cc: stable@vger.kernel.org
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/farch.c

@@ -835,14 +835,14 @@ efx_farch_handle_tx_event(struct efx_channel *channel, efx_qword_t *event)
 		/* Transmit completion */
 		tx_ev_desc_ptr = EFX_QWORD_FIELD(*event, FSF_AZ_TX_EV_DESC_PTR);
 		tx_ev_q_label = EFX_QWORD_FIELD(*event, FSF_AZ_TX_EV_Q_LABEL);
-		tx_queue = efx_channel_get_tx_queue(
-			channel, tx_ev_q_label % EFX_MAX_TXQ_PER_CHANNEL);
+		tx_queue = channel->tx_queue +
+				(tx_ev_q_label % EFX_MAX_TXQ_PER_CHANNEL);
 		efx_xmit_done(tx_queue, tx_ev_desc_ptr);
 	} else if (EFX_QWORD_FIELD(*event, FSF_AZ_TX_EV_WQ_FF_FULL)) {
 		/* Rewrite the FIFO write pointer */
 		tx_ev_q_label = EFX_QWORD_FIELD(*event, FSF_AZ_TX_EV_Q_LABEL);
-		tx_queue = efx_channel_get_tx_queue(
-			channel, tx_ev_q_label % EFX_MAX_TXQ_PER_CHANNEL);
+		tx_queue = channel->tx_queue +
+				(tx_ev_q_label % EFX_MAX_TXQ_PER_CHANNEL);
 
 		netif_tx_lock(efx->net_dev);
 		efx_farch_notify_tx_desc(tx_queue);