nilfs2: fix memory leak in nilfs_ioctl_clean_segments

This fixes a new memory leak problem in garbage collection.  The
problem was brought by the bugfix patch ("nilfs2: fix lock order
reversal in nilfs_clean_segments ioctl").

Thanks to Kentaro Suzuki for finding this problem.
Reported-by: Kentaro Suzuki <k_suzuki@ms.sylc.co.jp>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/ioctl.c

@@ -576,7 +576,7 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
 	ret = nilfs_clean_segments(inode->i_sb, argv, kbufs);
 
  out_free:
-	while (--n > 0)
+	while (--n >= 0)
 		vfree(kbufs[n]);
 	kfree(kbufs[4]);
 	return ret;