iommu/arm-smmu: fix null-pointer dereference in arm_smmu_add_device

Commit c54451a "iommu/arm-smmu: Fix the error path in arm_smmu_add_device"
removed fwspec assignment in legacy_binding path as redundant which is
wrong. It needs to be updated after fwspec initialisation in
arm_smmu_register_legacy_master() as it is dereferenced later. Without
this there is a NULL-pointer dereference panic during boot on some hosts.

Signed-off-by: Artem Savkov <asavkov@redhat.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/arm-smmu.c

@@ -1519,6 +1519,13 @@ static int arm_smmu_add_device(struct device *dev)
 
 	if (using_legacy_binding) {
 		ret = arm_smmu_register_legacy_master(dev, &smmu);
+
+		/*
+		 * If dev->iommu_fwspec is initally NULL, arm_smmu_register_legacy_master()
+		 * will allocate/initialise a new one. Thus we need to update fwspec for
+		 * later use.
+		 */
+		fwspec = dev->iommu_fwspec;
 		if (ret)
 			goto out_free;
 	} else if (fwspec && fwspec->ops == &arm_smmu_ops) {