nfs_common: move locks_in_grace comment at the right place

Commit c87fb4a3 ("lockd: NLM grace period shouldn't block NFSv4 opens")
made the locks_in_grace() comment be in the wrong place.

This patch move this comment just at the right place.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>