Use memset_startat() helper to simplify the code, no functional changes.

Link: https://lore.kernel.org/r/20220613021851.59699-1-xiujianfeng@huawei.comReviewed-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>