iommu/dart: check return value after calling platform_get_resource()

It will cause null-ptr-deref in resource_size(), if platform_get_resource()
returns NULL, move calling resource_size() after devm_ioremap_resource() that
will check 'res' to avoid null-ptr-deref.
And use devm_platform_get_and_ioremap_resource() to simplify code.

Fixes: 46d1fb07 ("iommu/dart: Add DART iommu driver")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Sven Peter <sven@svenpeter.dev>
Link: https://lore.kernel.org/r/20220425090826.2532165-1-yangyingliang@huawei.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/apple-dart.c

@@ -859,16 +859,15 @@ static int apple_dart_probe(struct platform_device *pdev)
 	dart->dev = dev;
 	spin_lock_init(&dart->lock);
 
-	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	dart->regs = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(dart->regs))
+		return PTR_ERR(dart->regs);
+
 	if (resource_size(res) < 0x4000) {
 		dev_err(dev, "MMIO region too small (%pr)\n", res);
 		return -EINVAL;
 	}
 
-	dart->regs = devm_ioremap_resource(dev, res);
-	if (IS_ERR(dart->regs))
-		return PTR_ERR(dart->regs);
-
 	dart->irq = platform_get_irq(pdev, 0);
 	if (dart->irq < 0)
 		return -ENODEV;