switch open-coded instances of d_make_root() to new helper

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 1e85a7a..81932fa 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -831,8 +831,6 @@
 static int
 hugetlbfs_fill_super(struct super_block *sb, void *data, int silent)
 {
-	struct inode * inode;
-	struct dentry * root;
 	int ret;
 	struct hugetlbfs_config config;
 	struct hugetlbfs_sb_info *sbinfo;
@@ -865,16 +863,9 @@
 	sb->s_magic = HUGETLBFS_MAGIC;
 	sb->s_op = &hugetlbfs_ops;
 	sb->s_time_gran = 1;
-	inode = hugetlbfs_get_root(sb, &config);
-	if (!inode)
+	sb->s_root = d_make_root(hugetlbfs_get_root(sb, &config));
+	if (!sb->s_root)
 		goto out_free;
-
-	root = d_alloc_root(inode);
-	if (!root) {
-		iput(inode);
-		goto out_free;
-	}
-	sb->s_root = root;
 	return 0;
 out_free:
 	kfree(sbinfo);