crypto: ahash - Zero positive err value in ahash_update_finish

crypto: ahash - Zero positive err value in ahash_update_finish

The partial block length returned by a block-only driver should
not be passed up to the caller since ahash itself deals with the
partial block data.

Set err to zero in ahash_update_finish if it was positive.

Reported-by: T Pratham <t-pratham@ti.com>
Tested-by: T Pratham <t-pratham@ti.com>
Fixes: 9d7a0ab1c753 ("crypto: ahash - Handle partial blocks in API")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>