erofs: derive fsid from on-disk UUID for .statfs() if possible

Use the superblock's UUID to generate the fsid when it's non-null.

Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Hongzhen Luo <hongzhen@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240409113022.74720-1-hongzhen@linux.alibaba.com


Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>