crypto: echainiv - Replace chaining with multiplication

The current implementation uses a global per-cpu array to store
data which are used to derive the next IV.  This is insecure as
the attacker may change the stored data.

This patch removes all traces of chaining and replaces it with
multiplication of the salt and the sequence number.

Fixes: a10f554f ("crypto: echainiv - Add encrypted chain IV...")
Cc: stable@vger.kernel.org
Reported-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>