liquidio: lowmem: do not dereference null ptr

Don't dereference a NULL ptr in octeon_droq_destroy_ring_buffers().
Signed-off-by: Rick Farrington <ricardo.farrington@cavium.com>
Signed-off-by: Satanand Burla <satananda.burla@cavium.com>
Signed-off-by: Raghu Vatsavayi <raghu.vatsavayi@cavium.com>
Signed-off-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cavium/liquidio/octeon_droq.c

@@ -145,6 +145,8 @@ octeon_droq_destroy_ring_buffers(struct octeon_device *oct,
 
 	for (i = 0; i < droq->max_count; i++) {
 		pg_info = &droq->recv_buf_list[i].pg_info;
+		if (!pg_info)
+			continue;
 
 		if (pg_info->dma)
 			lio_unmap_ring(oct->pci_dev,