ravb: Fix a typo in comment

Fix the typo RX->TX in comment, as the code following the comment
process TX and not RX.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/renesas/ravb_main.c

@@ -920,7 +920,7 @@ static int ravb_poll(struct napi_struct *napi, int budget)
 	if (ravb_rx(ndev, &quota, q))
 		goto out;
 
-	/* Processing RX Descriptor Ring */
+	/* Processing TX Descriptor Ring */
 	spin_lock_irqsave(&priv->lock, flags);
 	/* Clear TX interrupt */
 	ravb_write(ndev, ~(mask | TIS_RESERVED), TIS);