btrfs: simplify error handling at btrfs_del_root_ref()

At btrfs_del_root_ref() we are using two return variables, named 'ret'
and 'err'. This makes it harder to follow and easier to return the wrong
value in case an error happens - the previous patch in the series, which
has the subject "btrfs: fix silent failure when deleting root
reference", fixed a bug due to confusion created by these two variables.

So change the function to use a single variable for tracking the return
value of the function, using only 'ret', which is consistent with most
of the codebase.

Reviewed-by: Qu Wenruo <[e-mail]>
Signed-off-by: Filipe Manana <[e-mail]>
Reviewed-by: David Sterba <[e-mail]>
Signed-off-by: David Sterba <[e-mail]>

fs/btrfs/root-tree.c

···
 	struct extent_buffer *leaf;
 	struct btrfs_key key;
 	unsigned long ptr;
-	int err = 0;
 	int ret;
 
 	path = btrfs_alloc_path();
···
 again:
 	ret = btrfs_search_slot(trans, tree_root, &key, path, -1, 1);
 	if (ret < 0) {
-		err = ret;
 		goto out;
 	} else if (ret == 0) {
 		leaf = path->nodes[0];
···
 		if ((btrfs_root_ref_dirid(leaf, ref) != dirid) ||
 		    (btrfs_root_ref_name_len(leaf, ref) != name_len) ||
 		    memcmp_extent_buffer(leaf, name, ptr, name_len)) {
-			err = -ENOENT;
+			ret = -ENOENT;
 			goto out;
 		}
 		*sequence = btrfs_root_ref_sequence(leaf, ref);
 
 		ret = btrfs_del_item(trans, tree_root, path);
-		if (ret) {
-			err = ret;
+		if (ret)
 			goto out;
-		}
-	} else
-		err = -ENOENT;
+	} else {
+		ret = -ENOENT;
+		goto out;
+	}
 
 	if (key.type == BTRFS_ROOT_BACKREF_KEY) {
 		btrfs_release_path(path);
···
 
 out:
 	btrfs_free_path(path);
-	return err;
+	return ret;
 }
 
 /*