nilfs2: add missing error code in comment of nilfs_search_super_root

nilfs_search_super_root can return -ENOMEM, but this error code is not
described in its kernel-doc comment.  This fixes the discrepancy.
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/recovery.c

@@ -804,6 +804,8 @@ int nilfs_salvage_orphan_logs(struct the_nilfs *nilfs,
  * %-EINVAL - No valid segment found
  *
  * %-EIO - I/O error
+ *
+ * %-ENOMEM - Insufficient memory available.
  */
 int nilfs_search_super_root(struct the_nilfs *nilfs,
 			    struct nilfs_recovery_info *ri)