ath9k: fix TSF offset precision issue

Dividing the beacon interval by ATH_BCBUF (8) truncates the result for
the default beacon interval of 100.
Fix the calculation by moving the division after conversion from TU to
microseconds.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -279,13 +279,14 @@ static void ath9k_set_tsfadjust(struct ath_softc *sc, struct ieee80211_vif *vif)
 	struct ath_common *common = ath9k_hw_common(sc->sc_ah);
 	struct ath_beacon_config *cur_conf = &sc->cur_beacon_conf;
 	struct ath_vif *avp = (void *)vif->drv_priv;
-	u64 tsfadjust;
+	u32 tsfadjust;
 
 	if (avp->av_bslot == 0)
 		return;
 
-	tsfadjust = cur_conf->beacon_interval * avp->av_bslot / ATH_BCBUF;
-	avp->tsf_adjust = cpu_to_le64(TU_TO_USEC(tsfadjust));
+	tsfadjust = cur_conf->beacon_interval * avp->av_bslot;
+	tsfadjust = TU_TO_USEC(tsfadjust) / ATH_BCBUF;
+	avp->tsf_adjust = cpu_to_le64(tsfadjust);
 
 	ath_dbg(common, CONFIG, "tsfadjust is: %llu for bslot: %d\n",
 		(unsigned long long)tsfadjust, avp->av_bslot);