mtd: nand: omap2: fix return value check in omap_nand_probe()

In case of error, the function dma_request_chan() returns ERR_PTR() and
never returns NULL. The NULL test in the return value check should be
replaced with IS_ERR().

Fixes: aa7abd31 ('mtd: nand: omap2: Support parsing dma channel
information from DT')
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/omap2.c

@@ -1920,9 +1920,9 @@ static int omap_nand_probe(struct platform_device *pdev)
 		dma_cap_set(DMA_SLAVE, mask);
 		info->dma = dma_request_chan(pdev->dev.parent, "rxtx");
 
-		if (!info->dma) {
+		if (IS_ERR(info->dma)) {
 			dev_err(&pdev->dev, "DMA engine request failed\n");
-			err = -ENXIO;
+			err = PTR_ERR(info->dma);
 			goto return_error;
 		} else {
 			struct dma_slave_config cfg;