vfio: Use ERR_CAST() instead of open coding it

It's a small cleanup to use ERR_CAST() here.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio.c

@@ -382,7 +382,7 @@ static struct vfio_group *vfio_create_group(struct iommu_group *iommu_group)
 	if (IS_ERR(dev)) {
 		vfio_free_group_minor(minor);
 		vfio_group_unlock_and_free(group);
-		return (struct vfio_group *)dev; /* ERR_PTR */
+		return ERR_CAST(dev);
 	}
 
 	group->minor = minor;