Btrfs: check the return value of io_ctl_init()

It can return -ENOMEM.
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>

fs/btrfs/free-space-cache.c

@@ -637,7 +637,10 @@ int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
 	if (!num_entries)
 		return 0;
 
-	io_ctl_init(&io_ctl, inode, root);
+	ret = io_ctl_init(&io_ctl, inode, root);
+	if (ret)
+		return ret;
+
 	ret = readahead_cache(inode);
 	if (ret)
 		goto out;
@@ -851,7 +854,9 @@ int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
 	if (!i_size_read(inode))
 		return -1;
 
-	io_ctl_init(&io_ctl, inode, root);
+	ret = io_ctl_init(&io_ctl, inode, root);
+	if (ret)
+		return -1;
 
 	/* Get the cluster for this block_group if it exists */
 	if (block_group && !list_empty(&block_group->cluster_list))