ath10k: fix Tx status clearing

Too much of tx info was being cleared. This caused
issues in some setups with tx frame status
reporting.

This should fix some cases of stations not being
able to associate to ath10k AP.

Reported-By: Matti Laakso <malaakso@elisanet.fi>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>