crypto: hisilicon/sgl - add a comment for block size initialization

mainline inclusion
from mainline-v5.13-rc1
commit 51028c6e
category: bugfix
bugzilla: 173981
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=51028c6efa90ba4ab2311b0977287aac8c154f5b



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This seems "32" and "31" is obfuscating, It might be better to add a comment,
which explain it.

Signed-off-by: Kai Ye <yekai13@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Mingqiang Ling <lingmingqiang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>