crypto: talitos - fix ahash for multiple of blocksize

Correct ahash_process_req() to properly handle cases
where the total hash amount is a multiple of the blocksize.
The SEC must have some data to hash during the very last
descriptor operation; so up to one whole blocksize
of data is buffered until the final hash.

Signed-off-by: Lee Nipper <lee.nipper@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>