wcn36xx: Use kmemdup instead of duplicating it in wcn36xx_smd_process_ptt_msg_rsp

Replace calls to kmalloc followed by a memcpy with a direct call to
kmemdup.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>