rhashtable: fix false-positive lockdep splat on rhltable destruction

rhashtable: fix false-positive lockdep splat on rhltable destruction

Blamed commit removed ht->mutex usage during destruction but forgot to
switch rhashtable_free_one() to rcu_dereference_raw(), this triggers a
lockdep splat when an rhltable gets zapped.

Fixes: 09ae540e1d5c ("rhashtable: drop ht->mutex in rhashtable_free_and_destroy()")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>