mtd: nand: sh_flctl: use dma_mapping_error to check map errors

The return value of dma_map_single() should be checked by
dma_mapping_error(). However, in function flctl_dma_fifo0_transfer(), its
return value is checked against NULL, which could result in failures.
Signed-off-by: NPan Bian <bianpan2016@163.com>
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/nand/sh_flctl.c

@@ -411,7 +411,7 @@ static int flctl_dma_fifo0_transfer(struct sh_flctl *flctl, unsigned long *buf,
 
 	dma_addr = dma_map_single(chan->device->dev, buf, len, dir);
 
-	if (dma_addr)
+	if (!dma_mapping_error(chan->device->dev, dma_addr))
 		desc = dmaengine_prep_slave_single(chan, dma_addr, len,
 			tr_dir, DMA_PREP_INTERRUPT | DMA_CTRL_ACK);