ath10k: abort incomplete scatter-gather pci tx properly

This prevents leaving incomplete scatter-gather
transfer on CE rings which can lead firmware to
crash.

Reported-By: Avery Pennarun <apenwarr@gmail.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>