ethernet: micrel: fix some error codes

There were two issues here:
1) dma_mapping_error() return true/false but we want to return -ENOMEM
2) If dmaengine_prep_slave_sg() failed then "err" wasn't set but
   presumably that should be -ENOMEM as well.

I changed the success path to "return 0;" instead of "return ret;" for
clarity.

Fixes: 94fe8c68 ('ks8842: Support DMA when accessed via timberdale')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/micrel/ks8842.c

@@ -561,8 +561,8 @@ static int __ks8842_start_new_rx_dma(struct net_device *netdev)
 		sg_init_table(sg, 1);
 		sg_dma_address(sg) = dma_map_single(adapter->dev,
 			ctl->skb->data, DMA_BUFFER_SIZE, DMA_FROM_DEVICE);
-		err = dma_mapping_error(adapter->dev, sg_dma_address(sg));
-		if (unlikely(err)) {
+		if (dma_mapping_error(adapter->dev, sg_dma_address(sg))) {
+			err = -ENOMEM;
 			sg_dma_address(sg) = 0;
 			goto out;
 		}
@@ -572,8 +572,10 @@ static int __ks8842_start_new_rx_dma(struct net_device *netdev)
 		ctl->adesc = dmaengine_prep_slave_sg(ctl->chan,
 			sg, 1, DMA_DEV_TO_MEM, DMA_PREP_INTERRUPT);
 
-		if (!ctl->adesc)
+		if (!ctl->adesc) {
+			err = -ENOMEM;
 			goto out;
+		}
 
 		ctl->adesc->callback_param = netdev;
 		ctl->adesc->callback = ks8842_dma_rx_cb;
@@ -584,7 +586,7 @@ static int __ks8842_start_new_rx_dma(struct net_device *netdev)
 		goto out;
 	}
 
-	return err;
+	return 0;
 out:
 	if (sg_dma_address(sg))
 		dma_unmap_single(adapter->dev, sg_dma_address(sg),