ath10k: poll HTT send completion when CE 5 is unused

commit a70587b3 ("ath10k: configure copy engine 5 for HTT messages")
moved send completion polling under HTT Rx (CE 5) service routine. For
QCA6174 based devices copy engine 1 (CE 1) is used for HTT Rx instead
of CE 5. So send completion never be called. This is causing "failed to
transmit packet, dropping: -105" errors. Fix this by processing send
completion from CE 1 service routine instead of CE 5.

Fixes: a70587b3

 ("ath10k: configure copy engine 5 for HTT messages")
Tested-by: Ryan Hsu <ryanhsu@qca.qualcomm.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>