mtd: atmel_nand: fix wrong use of 0 as NULL

Fixing this error:
atmel_nand.c:718:20: warning: Using plain integer as NULL pointer
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Artem Bityutskiy <dedekind1@gmail.com>

drivers/mtd/nand/atmel_nand.c

@@ -588,7 +588,7 @@ static int __init atmel_nand_probe(struct platform_device *pdev)
 
 		dma_cap_zero(mask);
 		dma_cap_set(DMA_MEMCPY, mask);
-		host->dma_chan = dma_request_channel(mask, 0, NULL);
+		host->dma_chan = dma_request_channel(mask, NULL, NULL);
 		if (!host->dma_chan) {
 			dev_err(host->dev, "Failed to request DMA channel\n");
 			use_dma = 0;