ath6kl: Fix potential skb double free in ath6kl_wmi_sync_point()

skb given to ath6kl_control_tx() is owned by ath6kl_control_tx().
Calling function should not free the skb for error cases.
This is found during code review.

kvalo: fix a checkpatch warning in ath6kl_wmi_cmd_send()

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>