When we perform a walk in the completion function, we need to ensure
that it is atomic.

Fixes: ac3c8f36 ("crypto: lrw - Do not use auxiliary buffer")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>