exportfs: remove kernel-doc warnings in exportfs

Remove kernel-doc warning in exportfs:

fs/exportfs/expfs.c:395: warning: Function parameter or member 'parent'
not described in 'exportfs_encode_inode_fh'
Signed-off-by: Zhu Wang <wangzhu9@huawei.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/exportfs/expfs.c

@@ -386,6 +386,7 @@ static int export_encode_fh(struct inode *inode, struct fid *fid,
  * @inode:   the object to encode
  * @fid:     where to store the file handle fragment
  * @max_len: maximum length to store there
+ * @parent:  parent directory inode, if wanted
  * @flags:   properties of the requested file handle
  *
  * Returns an enum fid_type or a negative errno.