ath9k: Drop useless const on chanctx_event_delta() return type

drivers/net/wireless/ath/ath9k/channel.c:230: warning: type qualifiers ignored on function return type
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath9k/channel.c

@@ -226,7 +226,7 @@ static const char *chanctx_state_string(enum ath_chanctx_state state)
 	}
 }
 
-static const u32 chanctx_event_delta(struct ath_softc *sc)
+static u32 chanctx_event_delta(struct ath_softc *sc)
 {
 	u64 ms;
 	struct timespec ts, *old;