iommu/msm: Fix an incorrect NULL check on list iterator

The bug is here:
	if (!iommu || iommu->dev->of_node != spec->np) {

The list iterator value 'iommu' will *always* be set and non-NULL by
list_for_each_entry(), so it is incorrect to assume that the iterator
value will be NULL if the list is empty or no element is found (in fact,
it will point to a invalid structure object containing HEAD).

To fix the bug, use a new value 'iter' as the list iterator, while use
the old value 'iommu' as a dedicated variable to point to the found one,
and remove the unneeded check for 'iommu->dev->of_node != spec->np'
outside the loop.

Cc: stable@vger.kernel.org
Fixes: f78ebca ("iommu/msm: Add support for generic master bindings")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Link: https://lore.kernel.org/r/20220501132823.12714-1-xiam0nd.tong@gmail.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: Xiaomeng Tong

drivers/iommu/msm_iommu.c

@@ -615,16 +615,19 @@ static int insert_iommu_master(struct device *dev,
 static int qcom_iommu_of_xlate(struct device *dev,
 			       struct of_phandle_args *spec)
 {
-	struct msm_iommu_dev *iommu;
+	struct msm_iommu_dev *iommu = NULL, *iter;
 	unsigned long flags;
 	int ret = 0;
 
 	spin_lock_irqsave(&msm_iommu_lock, flags);
-	list_for_each_entry(iommu, &qcom_iommu_devices, dev_node)
-		if (iommu->dev->of_node == spec->np)
+	list_for_each_entry(iter, &qcom_iommu_devices, dev_node) {
+		if (iter->dev->of_node == spec->np) {
+			iommu = iter;
 			break;
+		}
+	}
 
-	if (!iommu || iommu->dev->of_node != spec->np) {
+	if (!iommu) {
 		ret = -ENODEV;
 		goto fail;
 	}