ath9k: ar9002_phy: mark expected switch fall-throughs

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: NGustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/ath9k/ar9002_phy.c

@@ -119,7 +119,7 @@ static int ar9002_hw_set_channel(struct ath_hw *ah, struct ath9k_channel *chan)
 				aModeRefSel = 2;
 			if (aModeRefSel)
 				break;
-			/* else: fall through */
+			/* fall through */
 		case 1:
 		default:
 			aModeRefSel = 0;