iommu/arm-smmu: fix possible null-ptr-deref in arm_smmu_device_probe()

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

Signed-off-by: Yang Yingliang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: Yang Yingliang

drivers/iommu/arm/arm-smmu/arm-smmu.c

@@ -2092,11 +2092,10 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
 	if (err)
 		return err;
 
-	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	ioaddr = res->start;
-	smmu->base = devm_ioremap_resource(dev, res);
+	smmu->base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
 	if (IS_ERR(smmu->base))
 		return PTR_ERR(smmu->base);
+	ioaddr = res->start;
 	/*
 	 * The resource size should effectively match the value of SMMU_TOP;
 	 * stash that temporarily until we know PAGESIZE to validate it with.