virtio: simplify the using of received in virtnet_poll

received is 0, no need to minus it and use "+=" to reassign it
Signed-off-by: NLi RongQing <roy.qing.li@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -749,9 +749,9 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 {
 	struct receive_queue *rq =
 		container_of(napi, struct receive_queue, napi);
-	unsigned int r, received = 0;
+	unsigned int r, received;
 
-	received += virtnet_receive(rq, budget - received);
+	received = virtnet_receive(rq, budget);
 
 	/* Out of packets? */
 	if (received < budget) {