rsi: add fix for corruption of auto rate table

Auto rate table sent to firmware is getting corrupted
as memset to zeros is not done. Added memset to skb
data before filling auto rate table.

Signed-off-by: Sanjay Konduri <sanjay.konduri@redpinesignals.com>
Signed-off-by: Sushant Kumar Mishra <sushant.mishra@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>