iommu/amd: Handle race between registration and device probe

As for the Intel driver, make sure the AMD driver can cope with seeing
.probe_device calls without having to wait for all known instances to
register first.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/a8d8ebe12b411d28972f1ab928c6db92e8913cf5.1660572783.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/amd/iommu.c

@@ -1851,6 +1851,10 @@ static struct iommu_device *amd_iommu_probe_device(struct device *dev)
 	if (!iommu)
 		return ERR_PTR(-ENODEV);
 
+	/* Not registered yet? */
+	if (!iommu->iommu.ops)
+		return ERR_PTR(-ENODEV);
+
 	if (dev_iommu_priv_get(dev))
 		return &iommu->iommu;