blk-cgroup: add spin_lock for u64_stats_update

[Boy Wu (吳勃誼)]

On Mon, 2024-07-08 at 07:43 +0200, Markus Elfring wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  > ************* MEDIATEK Confidentiality Notice ********************
> …
> 
> Please omit such information from your patches for Linux software
> components.
> Such hints do probably not fit to communication characteristics of
> Linux mailing lists.
> 
> Regards,
> Markus

The email system removing disclaimer is fixed. Can check with patch v2.

Boy.Wu