iommu: Propagate error in add_iommu_group

Make sure any errors reported from the IOMMU drivers get
progapated back to the IOMMU core.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 755e488..9c9336a 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -750,9 +750,7 @@
 
 	WARN_ON(dev->iommu_group);
 
-	ops->add_device(dev);
-
-	return 0;
+	return ops->add_device(dev);
 }
 
 static int iommu_bus_notifier(struct notifier_block *nb,