crypto: hisilicon/hpre - remove useless code

1. Remove unused member 'debug_root' in 'struct hpre_debug';
2. The u64 cast is redundant in 'cpu_to_le64'.

Fixes: 84897415("crypto: hisilicon - Add debugfs for HPRE")
Fixes: dadbe4c1("crypto: hisilicon/hpre - update debugfs ...")
Signed-off-by: Meng Yu <yumeng18@huawei.com>
Reviewed-by: Zaibo Xu <xuzaibo@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>