ath9k: Fix compile warnings when DEBUGFS is disabled.

This fixes two compile warnings, and removes a useless
cast when assigning the 'sc' variable.

Reported-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -959,7 +959,8 @@ bool ath9k_hw_setpower(struct ath_hw *ah, enum ath9k_power_mode mode);
 #ifdef CONFIG_ATH9K_DEBUGFS
 void ath9k_debug_sync_cause(struct ath_common *common, u32 sync_cause);
 #else
-static void ath9k_debug_sync_cause(struct ath_common *common, u32 sync_cause) {}
+static inline void ath9k_debug_sync_cause(struct ath_common *common,
+					  u32 sync_cause) {}
 #endif
 
 /* Generic hw timer primitives */