crypto: hisilicon - misc fix about sgl

This patch fixes some misc problems in sgl codes, e.g. missing static,
sparse error and input parameter check.

Signed-off-by: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Shukun Tan <tanshukun1@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>