ath9k_hw: set 5 GHz half/quarter channels on AR9002 using fractional mode

The radio seems to perform better that way
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/ar9002_phy.c

@@ -111,7 +111,9 @@ static int ar9002_hw_set_channel(struct ath_hw *ah, struct ath9k_channel *chan)
 
 		switch (ah->eep_ops->get_eeprom(ah, EEP_FRAC_N_5G)) {
 		case 0:
-			if ((freq % 20) == 0)
+			if (IS_CHAN_HALF_RATE(chan) || IS_CHAN_QUARTER_RATE(chan))
+				aModeRefSel = 0;
+			else if ((freq % 20) == 0)
 				aModeRefSel = 3;
 			else if ((freq % 10) == 0)
 				aModeRefSel = 2;