vfio: Fix handling of error returned by 'vfio_group_get_from_dev()'

'vfio_group_get_from_dev()' seems to return only NULL on error, not an
error pointer.

Fixes: 2169037d ("vfio iommu: Added pin and unpin callback functions to vfio_iommu_driver_ops")
Fixes: c086de81 ("vfio iommu: Add blocking notifier to notify DMA_UNMAP")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio.c

@@ -1933,8 +1933,8 @@ int vfio_pin_pages(struct device *dev, unsigned long *user_pfn, int npage,
 		return -E2BIG;
 
 	group = vfio_group_get_from_dev(dev);
-	if (IS_ERR(group))
-		return PTR_ERR(group);
+	if (!group)
+		return -ENODEV;
 
 	ret = vfio_group_add_container_user(group);
 	if (ret)
@@ -1982,8 +1982,8 @@ int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn, int npage)
 		return -E2BIG;
 
 	group = vfio_group_get_from_dev(dev);
-	if (IS_ERR(group))
-		return PTR_ERR(group);
+	if (!group)
+		return -ENODEV;
 
 	ret = vfio_group_add_container_user(group);
 	if (ret)
@@ -2019,8 +2019,8 @@ int vfio_register_notifier(struct device *dev, struct notifier_block *nb)
 		return -EINVAL;
 
 	group = vfio_group_get_from_dev(dev);
-	if (IS_ERR(group))
-		return PTR_ERR(group);
+	if (!group)
+		return -ENODEV;
 
 	ret = vfio_group_add_container_user(group);
 	if (ret)
@@ -2055,8 +2055,8 @@ int vfio_unregister_notifier(struct device *dev, struct notifier_block *nb)
 		return -EINVAL;
 
 	group = vfio_group_get_from_dev(dev);
-	if (IS_ERR(group))
-		return PTR_ERR(group);
+	if (!group)
+		return -ENODEV;
 
 	ret = vfio_group_add_container_user(group);
 	if (ret)