ath9k: Fix symbol overlap window for half/quarter channels

Since commit cd6cfd7311a385144a2f9c74f692ae2df3ae033f
"ath9k: do not set half/quarter channel flags in AR_PHY_MODE" the
condition "rfMode & (AR_PHY_MODE_QUARTER | AR_PHY_MODE_HALF)" would
never evaluate to true.

Fix this by using the available IS_CHAN_HALF_RATE and IS_CHAN_QUARTER_RATE
marcros instead.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Cc: Felix Fietkau <nbd@openwrt.org>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath9k/ar9003_phy.c

@@ -1010,7 +1010,7 @@ static void ar9003_hw_set_rfmode(struct ath_hw *ah,
 	if (IS_CHAN_A_FAST_CLOCK(ah, chan))
 		rfMode |= (AR_PHY_MODE_DYNAMIC | AR_PHY_MODE_DYN_CCK_DISABLE);
 
-	if (rfMode & (AR_PHY_MODE_QUARTER | AR_PHY_MODE_HALF))
+	if (IS_CHAN_HALF_RATE(chan) || IS_CHAN_QUARTER_RATE(chan))
 		REG_RMW_FIELD(ah, AR_PHY_FRAME_CTL,
 			      AR_PHY_FRAME_CTL_CF_OVERLAP_WINDOW, 3);