wcn36xx: Remove unnecessary memset

memcpy operation is next to memset code, and the size to copy is equals to the size to
memset, so the memset operation is unnecessary, remove it.

Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201223012516.24286-1-zhengyongjun3@huawei.com