ath9k: hw: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 1056532 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

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

@@ -2279,6 +2279,7 @@ void ath9k_hw_beaconinit(struct ath_hw *ah, u32 next_beacon, u32 beacon_period)
 	case NL80211_IFTYPE_ADHOC:
 		REG_SET_BIT(ah, AR_TXCFG,
 			    AR_TXCFG_ADHOC_BEACON_ATIM_TX_POLICY);
+		/* fall through */
 	case NL80211_IFTYPE_MESH_POINT:
 	case NL80211_IFTYPE_AP:
 		REG_WRITE(ah, AR_NEXT_TBTT_TIMER, next_beacon);