vhost_vdpa: return -EFAULT if copy_to_user() fails

The copy_to_user() function returns the number of bytes remaining to be
copied but this should return -EFAULT to the user.

Fixes: 1b48dc0 ("vhost: vdpa: report iova range")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/X8c32z5EtDsMyyIL@mwanda
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

drivers/vhost/vdpa.c

@@ -348,7 +348,9 @@ static long vhost_vdpa_get_iova_range(struct vhost_vdpa *v, u32 __user *argp)
 		.last = v->range.last,
 	};
 
-	return copy_to_user(argp, &range, sizeof(range));
+	if (copy_to_user(argp, &range, sizeof(range)))
+		return -EFAULT;
+	return 0;
 }
 
 static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,