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>

drivers/net/wireless/ath/ath9k/hw.h

@@ -455,7 +455,6 @@ struct ath9k_channel {
 	 ((_ah)->caps.hw_caps & ATH9K_HW_CAP_FASTCLOCK))
 
 /* These macros check chanmode and not channelFlags */
-#define IS_CHAN_B(_c) ((_c)->chanmode == CHANNEL_B)
 #define IS_CHAN_HT20(_c) (((_c)->chanmode == CHANNEL_A_HT20) ||	\
 			  ((_c)->chanmode == CHANNEL_G_HT20))
 #define IS_CHAN_HT40(_c) (((_c)->chanmode == CHANNEL_A_HT40PLUS) ||	\