struct filename ->refcnt doesn't need to be atomic

... or visible outside of audit, really.  Note that references
held in delayed_filename always have refcount 1, and from the
moment of complete_getname() or equivalent point in getname...()
there won't be any references to struct filename instance left
in places visible to other threads.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>