ath6kl: Remove unneeded memset in roam related config func

No need to clear requested memory after allocating new SKB
with help of ath6kl_wmi_get_new_buf(). This clear part is
already taken care in ath6kl_wmi_get_new_buf().

Found this on code review.

Signed-off-by: Raja Mani <rmani@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>