erofs: convert to use super_set_uuid to support for FS_IOC_GETFSUUID

FS_IOC_GETFSUUID ioctl exposes the uuid of a filesystem. To support
the ioctl, init sb->s_uuid with super_set_uuid().

Signed-off-by: Huang Xiaojia <huangxiaojia2@huawei.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20240624063704.2476070-1-huangxiaojia2@huawei.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>