ath10k: use num_pending_tx instead of msdu id bitmap

It's more efficient to simply check num_pending_tx
value instead of traversing whole bitmap of
msdu ids.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

diff --cc drivers/net/wireless/ath/ath10k/mac.c
Simple merge

diff --cc drivers/net/wireless/ath/ath10k/txrx.c
Simple merge