ath10k: check for encryption before adding MIC_LEN

In the case of raw mode without nohwcrypt parameter, we
should still make sure the frame is protected before
adding MIC_LEN to avoid skb_under_panic errors.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>