ath9k: Cleanup ineffective return values

This patch makes the return type of some of the functions
void as those functions always return true

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/eeprom.h b/drivers/net/wireless/ath/ath9k/eeprom.h
index 7c59dc4..67b8bd1 100644
--- a/drivers/net/wireless/ath/ath9k/eeprom.h
+++ b/drivers/net/wireless/ath/ath9k/eeprom.h
@@ -494,7 +494,7 @@
 				      struct ath9k_channel *chan);
 	void (*set_board_values)(struct ath_hw *hw, struct ath9k_channel *chan);
 	void (*set_addac)(struct ath_hw *hw, struct ath9k_channel *chan);
-	int (*set_txpower)(struct ath_hw *hw, struct ath9k_channel *chan,
+	void (*set_txpower)(struct ath_hw *hw, struct ath9k_channel *chan,
 			   u16 cfgCtl, u8 twiceAntennaReduction,
 			   u8 twiceMaxRegulatoryPower, u8 powerLimit);
 	u16 (*get_spur_channel)(struct ath_hw *ah, u16 i, bool is2GHz);