tg3: Apply rx_discards fix to 5719/5720

Commit 4d958473, entitled
"tg3: Workaround rx_discards stat bug", was intended to be applied to
the 5717, 5718, 5719_A0, and 5720 A0 chip revisions.  The implementation
missed the latter two when applying the fix in a critical area.  This
patch fixes the problem.
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tg3.c

@@ -8797,7 +8797,9 @@ static void tg3_periodic_fetch_stats(struct tg3 *tp)
 	TG3_STAT_ADD32(&sp->rx_undersize_packets, MAC_RX_STATS_UNDERSIZE);
 
 	TG3_STAT_ADD32(&sp->rxbds_empty, RCVLPC_NO_RCV_BD_CNT);
-	if (GET_ASIC_REV(tp->pci_chip_rev_id) != ASIC_REV_5717) {
+	if (GET_ASIC_REV(tp->pci_chip_rev_id) != ASIC_REV_5717 &&
+	    tp->pci_chip_rev_id != CHIPREV_ID_5719_A0 &&
+	    tp->pci_chip_rev_id != CHIPREV_ID_5720_A0) {
 		TG3_STAT_ADD32(&sp->rx_discards, RCVLPC_IN_DISCARDS_CNT);
 	} else {
 		u32 val = tr32(HOSTCC_FLOW_ATTN);