ath9k: make the driver specific rate control module optional

ath9k can use minstrel_ht instead, so it makes sense to save some space here.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -224,7 +224,18 @@ enum ath9k_internal_frame_type {
 	ATH9K_IFT_UNPAUSE
 };
 
+#ifdef CONFIG_ATH9K_RATE_CONTROL
 int ath_rate_control_register(void);
 void ath_rate_control_unregister(void);
+#else
+static inline int ath_rate_control_register(void)
+{
+	return 0;
+}
+
+static inline void ath_rate_control_unregister(void)
+{
+}
+#endif
 
 #endif /* RC_H */