crypto: ahash - Disable request chaining

Disable hash request chaining in case a driver that copies an
ahash_request object by hand accidentally triggers chaining.

Reported-by: Manorit Chawdhry <m-chawdhry@ti.com>
Fixes: f2ffe5a9 ("crypto: hash - Add request chaining API")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Manorit Chawdhry <m-chawdhry@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>