iommu: Return ERR_PTR() values from device_group call-backs

The generic device_group call-backs in iommu.c return NULL
in case of error. Since they are getting ERR_PTR values from
iommu_group_alloc(), just pass them up instead.
Reported-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -915,13 +915,7 @@ static int get_pci_alias_or_group(struct pci_dev *pdev, u16 alias, void *opaque)
  */
 struct iommu_group *generic_device_group(struct device *dev)
 {
-	struct iommu_group *group;
-
-	group = iommu_group_alloc();
-	if (IS_ERR(group))
-		return NULL;
-
-	return group;
+	return iommu_group_alloc();
 }
 
 /*
@@ -988,11 +982,7 @@ struct iommu_group *pci_device_group(struct device *dev)
 		return group;
 
 	/* No shared group found, allocate new */
-	group = iommu_group_alloc();
-	if (IS_ERR(group))
-		return NULL;
-
-	return group;
+	return iommu_group_alloc();
 }
 
 /**