ath9k: fix ready time of the multicast buffer queue

commit 3b3e0efb upstream.

qi->tqi_readyTime is written directly to registers that expect
microseconds as unit instead of TU.
When setting the CABQ ready time, cur_conf->beacon_interval is in TU, so
convert it to microseconds before passing it to ath9k_hw.

This should hopefully fix some Tx DMA issues with buffered multicast
frames in AP mode.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

drivers/net/wireless/ath/ath9k/xmit.c

@@ -1718,7 +1718,7 @@ int ath_cabq_update(struct ath_softc *sc)
 	else if (sc->config.cabqReadytime > ATH9K_READY_TIME_HI_BOUND)
 		sc->config.cabqReadytime = ATH9K_READY_TIME_HI_BOUND;
 
-	qi.tqi_readyTime = (cur_conf->beacon_interval *
+	qi.tqi_readyTime = (TU_TO_USEC(cur_conf->beacon_interval) *
 			    sc->config.cabqReadytime) / 100;
 	ath_txq_update(sc, qnum, &qi);