soc: ixp4xx: qmgr: Fix an NULL vs IS_ERR() check in probe

The devm_ioremap_resource() function doesn't retunr NULL, it returns
error pointers.

Fixes: ecc133c6 ("soc: ixp4xx: qmgr: Pass resources")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NOlof Johansson <olof@lixom.net>

drivers/soc/ixp4xx/ixp4xx-qmgr.c

@@ -385,8 +385,8 @@ static int ixp4xx_qmgr_probe(struct platform_device *pdev)
 	if (!res)
 		return -ENODEV;
 	qmgr_regs = devm_ioremap_resource(dev, res);
-	if (!qmgr_regs)
-		return -ENOMEM;
+	if (IS_ERR(qmgr_regs))
+		return PTR_ERR(qmgr_regs);
 
 	irq1 = platform_get_irq(pdev, 0);
 	if (irq1 <= 0)