gpio-ml-ioh: cleanup NULL pointer checking

This patch will remove the following sparse warning ("make C=1"):
 * warning: Using plain integer as NULL pointer
Signed-off-by: Márton Németh <nm127@freemail.hu>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/gpio/gpio-ml-ioh.c

@@ -428,7 +428,7 @@ static int __devinit ioh_gpio_probe(struct pci_dev *pdev,
 	}
 
 	base = pci_iomap(pdev, 1, 0);
-	if (base == 0) {
+	if (!base) {
 		dev_err(&pdev->dev, "%s : pci_iomap failed", __func__);
 		ret = -ENOMEM;
 		goto err_iomap;