ath10k: htc: made static function public

Changed ath10k_htc_notify_tx_completion and
ath10k_htc_process_trailer from static to non static.

These functions are needed by SDIO/mbox.

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>