erofs: fix metabuf leak in inode xattr initialization

commit bb88e8da0025 ("erofs: use meta buffers for xattr operations")
converted xattr operations to use on-stack erofs_buf instances.
erofs_init_inode_xattrs() uses such a metabuf while reading the inline
xattr header and shared xattr id array.

Some error paths after erofs_read_metabuf() leave through out_unlock
without dropping the metabuf, so the folio reference can leak.

Consolidate the cleanup at out_unlock. erofs_put_metabuf() is a
no-op if no folio has been acquired, and this keeps all paths after
taking EROFS_I_BL_XATTR_BIT covered by a single cleanup site.

Fixes: bb88e8da0025 ("erofs: use meta buffers for xattr operations")
Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Fixes: bb88e8da0025 ("erofs: use meta buffers for xattr operations")
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>