ath9k: Fix a sparse warning

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c
index 4ff155e..c039d0a 100644
--- a/drivers/net/wireless/ath/ath9k/xmit.c
+++ b/drivers/net/wireless/ath/ath9k/xmit.c
@@ -2037,7 +2037,7 @@
 	}
 }
 
-void ath_tx_complete_poll_work(struct work_struct *work)
+static void ath_tx_complete_poll_work(struct work_struct *work)
 {
 	struct ath_softc *sc = container_of(work, struct ath_softc,
 			tx_complete_work.work);