ath9k_hw: fix MAC clock for half/quarter rate

Enabling half/quarter rate makes the MAC run at half/quarter clock speed.

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/hw.c b/drivers/net/wireless/ath/ath9k/hw.c
index a6bb9c4..f69c62e 100644
--- a/drivers/net/wireless/ath/ath9k/hw.c
+++ b/drivers/net/wireless/ath/ath9k/hw.c
@@ -99,6 +99,13 @@
 	if (conf_is_ht40(conf))
 		clockrate *= 2;
 
+	if (ah->curchan) {
+		if (IS_CHAN_HALF_RATE(ah->curchan))
+			clockrate /= 2;
+		if (IS_CHAN_QUARTER_RATE(ah->curchan))
+			clockrate /= 4;
+	}
+
 	common->clockrate = clockrate;
 }