net: fec: use managed DMA API functions to allocate BD ring

So it gets freed when the device is going away.
This fixes a DMA memory leak on driver probe() fail and driver
remove().

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_main.c

@@ -3115,8 +3115,8 @@ static int fec_enet_init(struct net_device *ndev)
 			fep->bufdesc_size;
 
 	/* Allocate memory for buffer descriptors. */
-	cbd_base = dma_alloc_coherent(NULL, bd_size, &bd_dma,
-				      GFP_KERNEL);
+	cbd_base = dmam_alloc_coherent(&fep->pdev->dev, bd_size, &bd_dma,
+				       GFP_KERNEL);
 	if (!cbd_base) {
 		return -ENOMEM;
 	}