btrfs: make open_ctree() return int

It returns either ERR_PTR(-ve) or sb->s_fs_info.  The latter can
be found by caller just as well, TYVM, no need to return it.  Just
return -ve or 0...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index e9f876a..56e007f 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -604,12 +604,12 @@
 	sb->s_flags |= MS_POSIXACL;
 #endif
 
-	tree_root = open_ctree(sb, fs_devices, (char *)data);
-
-	if (IS_ERR(tree_root)) {
+	err = open_ctree(sb, fs_devices, (char *)data);
+	if (err) {
 		printk("btrfs: open_ctree failed\n");
-		return PTR_ERR(tree_root);
+		return err;
 	}
+	tree_root = sb->s_fs_info;
 	fs_info = tree_root->fs_info;
 	sb->s_fs_info = tree_root;