ath9k_hw: increase symbol overlap window for half/quarter channels

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/ar9003_phy.c b/drivers/net/wireless/ath/ath9k/ar9003_phy.c
index be6069b..4c8d0d7 100644
--- a/drivers/net/wireless/ath/ath9k/ar9003_phy.c
+++ b/drivers/net/wireless/ath/ath9k/ar9003_phy.c
@@ -728,6 +728,10 @@
 	if (IS_CHAN_HALF_RATE(chan))
 		rfMode |= AR_PHY_MODE_HALF;
 
+	if (rfMode & (AR_PHY_MODE_QUARTER | AR_PHY_MODE_HALF))
+		REG_RMW_FIELD(ah, AR_PHY_FRAME_CTL,
+			      AR_PHY_FRAME_CTL_CF_OVERLAP_WINDOW, 3);
+
 	REG_WRITE(ah, AR_PHY_MODE, rfMode);
 }