ath9k: use u8 for the tx key index

This saves some space in struct ath_frame_info

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/hw.h b/drivers/net/wireless/ath/ath9k/hw.h
index 3aa3fb1..c8af86c 100644
--- a/drivers/net/wireless/ath/ath9k/hw.h
+++ b/drivers/net/wireless/ath/ath9k/hw.h
@@ -623,7 +623,7 @@
 			   struct ath_tx_status *ts);
 	void (*set11n_txdesc)(struct ath_hw *ah, void *ds,
 			      u32 pktLen, enum ath9k_pkt_type type,
-			      u32 txPower, u32 keyIx,
+			      u32 txPower, u8 keyIx,
 			      enum ath9k_key_type keyType,
 			      u32 flags);
 	void (*set11n_ratescenario)(struct ath_hw *ah, void *ds,