hugetlbfs: fix inaccurate comment in hugetlbfs_statfs()

In some cases, e.g.  when size option is not specified, f_blocks, f_bavail
and f_bfree will be set to -1 instead of 0.  Likewise, when nr_inodes
isn't specified, f_files and f_ffree will be set to -1 too.  Update the
comment to make this clear.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Miaohe Lin <[email protected]>
Reviewed-by: Mike Kravetz <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

fs/hugetlbfs/inode.c

@@ -1090,7 +1090,7 @@ static int hugetlbfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	buf->f_bsize = huge_page_size(h);
 	if (sbinfo) {
 		spin_lock(&sbinfo->stat_lock);
-		/* If no limits set, just report 0 for max/free/used
+		/* If no limits set, just report 0 or -1 for max/free/used
 		 * blocks, like simple_statfs() */
 		if (sbinfo->spool) {
 			long free_pages;