spi: atmel: fix return value check in atmel_spi_probe()

In case of error, the function devm_ioremap_resource() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check should be
replaced with IS_ERR().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/spi-atmel.c

@@ -1547,8 +1547,10 @@ static int atmel_spi_probe(struct platform_device *pdev)
 
 	as->pdev = pdev;
 	as->regs = devm_ioremap_resource(&pdev->dev, regs);
-	if (!as->regs)
+	if (IS_ERR(as->regs)) {
+		ret = PTR_ERR(as->regs);
 		goto out_free_buffer;
+	}
 	as->phybase = regs->start;
 	as->irq = irq;
 	as->clk = clk;