ath9k_hw: remove IS_CHAN_B()

Hardware 802.11b-only mode isn't supported by the driver (the device is
configured for 802.11n/g instead). Simplify the code by removing checks
for it.

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/ar5008_phy.c b/drivers/net/wireless/ath/ath9k/ar5008_phy.c
index 2bfa6fb..b197bf2 100644
--- a/drivers/net/wireless/ath/ath9k/ar5008_phy.c
+++ b/drivers/net/wireless/ath/ath9k/ar5008_phy.c
@@ -794,8 +794,10 @@
 	if (chan == NULL)
 		return;
 
-	rfMode |= (IS_CHAN_B(chan) || IS_CHAN_G(chan))
-		? AR_PHY_MODE_DYNAMIC : AR_PHY_MODE_OFDM;
+	if (IS_CHAN_2GHZ(chan))
+		rfMode |= AR_PHY_MODE_DYNAMIC;
+	else
+		rfMode |= AR_PHY_MODE_OFDM;
 
 	if (!AR_SREV_9280_20_OR_LATER(ah))
 		rfMode |= (IS_CHAN_5GHZ(chan)) ?