vfio/mlx5: fix error code in mlx5vf_precopy_ioctl()

The copy_to_user() function returns the number of bytes remaining to
be copied but we want to return a negative error code here.

Fixes: 0dce165 ("vfio/mlx5: Introduce vfio precopy ioctl implementation")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/Y5IKVknlf5Z5NPtU@kili
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Author: error27

drivers/vfio/pci/mlx5/main.c

@@ -404,7 +404,10 @@ static long mlx5vf_precopy_ioctl(struct file *filp, unsigned int cmd,
 
 done:
 	mlx5vf_state_mutex_unlock(mvdev);
-	return copy_to_user((void __user *)arg, &info, minsz);
+	if (copy_to_user((void __user *)arg, &info, minsz))
+		return -EFAULT;
+	return 0;
+
 err_migf_unlock:
 	mutex_unlock(&migf->lock);
 err_state_unlock: