net: mvpp2: Adjust a null pointer check in mvpp2_egress_enable()

The script "checkpatch.pl" pointed information out like the following.

Comparison to NULL could be written "txq->descs".

Thus fix the affected source code place.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvpp2.c

@@ -4415,7 +4415,7 @@ static void mvpp2_egress_enable(struct mvpp2_port *port)
 	for (queue = 0; queue < txq_number; queue++) {
 		struct mvpp2_tx_queue *txq = port->txqs[queue];
 
-		if (txq->descs != NULL)
+		if (txq->descs)
 			qmap |= (1 << queue);
 	}