ath10k: protect src_ring state with ce_lock in tx_sg()

It was possible to read invalid state of CE ring
buffer indexes. This could lead to scatter-gather
transfer failure in mid-way and crash firmware
later by leaving garbage data on the ring.

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>
ath10k: revert incomplete scatter-gather pci tx

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>
ath10k: add explicit memory barrier for ring index update

Avery reported he had some issues related to
instructions being re-ordered on his ARM test
system resulting in firmware crashes.

This makes sure that data is in place before CE
ring index is updated telling firmware it can
fetch the data.

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>