ath10k: fix return value check in wake_tx_q op

ath10k_mac_tx_push_txq returns either a postive integer (length) on
success or a negative error code on error.

The "if (ret) break;" statement will thus always break out of the loop
immediately after ath10k_mac_tx_push_txq has returned (making the loop
pointless).

A side effect of this fix is that we will iterate the queue until
ath10k_mac_tx_push_txq returns -ENOENT. This will make sure the queue is
not added back to ar->txqs when it is empty. This could potentially
improve performance somewhat (I have seen a small improvement with SDIO
devices).
Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/ath10k/mac.c

@@ -4290,7 +4290,7 @@ static void ath10k_mac_op_wake_tx_queue(struct ieee80211_hw *hw,
 
 	while (ath10k_mac_tx_can_push(hw, f_txq) && max--) {
 		ret = ath10k_mac_tx_push_txq(hw, f_txq);
-		if (ret)
+		if (ret < 0)
 			break;
 	}
 	if (ret != -ENOENT)