niu: Fix to check for dma mapping errors.

Fix Neptune ethernet driver to check dma mapping error after map_page()
interface returns.

Signed-off-by: Shuah Khan <shuah.khan@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/sun/niu.c b/drivers/net/ethernet/sun/niu.c
index 8c726b7..60d5c03 100644
--- a/drivers/net/ethernet/sun/niu.c
+++ b/drivers/net/ethernet/sun/niu.c
@@ -3335,6 +3335,10 @@
 
 	addr = np->ops->map_page(np->device, page, 0,
 				 PAGE_SIZE, DMA_FROM_DEVICE);
+	if (!addr) {
+		__free_page(page);
+		return -ENOMEM;
+	}
 
 	niu_hash_page(rp, page, addr);
 	if (rp->rbr_blocks_per_page > 1)