ath9k_htc: fix build with disabled debug

  CC [M]  drivers/net/wireless/ath/ath9k/htc_drv_txrx.o
drivers/net/wireless/ath/ath9k/htc_drv_txrx.c: In function ‘ath9k_rx_prepare’:
drivers/net/wireless/ath/ath9k/htc_drv_txrx.c:1006:2: warning: passing argument 2 of ‘ath9k_htc_err_stat_rx’ from incompatible pointer type [enabled by default]
  ath9k_htc_err_stat_rx(priv, &rx_stats);
  ^
In file included from drivers/net/wireless/ath/ath9k/htc_drv_txrx.c:17:0:
drivers/net/wireless/ath/ath9k/htc.h:380:20: note: expected ‘struct ath_htc_rx_status *’ but argument is of type ‘struct ath_rx_status *’
 static inline void ath9k_htc_err_stat_rx(struct ath9k_htc_priv *priv,
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -378,7 +378,7 @@ void ath9k_htc_get_et_stats(struct ieee80211_hw *hw,
 #define TX_QSTAT_INC(c) do { } while (0)
 
 static inline void ath9k_htc_err_stat_rx(struct ath9k_htc_priv *priv,
-					 struct ath_htc_rx_status *rxs)
+					 struct ath_rx_status *rs);
 {
 }