crypto: hisilicon/hpre - Use helper to set reqsize

The value of reqsize must only be changed through the helper.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Longfang Liu <liulongfang@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>