HSI: ssi_protocol: Mark expected switch fall-throughs

Mark switch cases where we are expecting to fall through.

This patch fixes the following warning (Building: arm):

drivers/hsi/clients/ssi_protocol.c: In function ‘ssip_set_rxstate’:
drivers/hsi/clients/ssi_protocol.c:291:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if (atomic_read(&ssi->tx_usecnt))
      ^
drivers/hsi/clients/ssi_protocol.c:294:2: note: here
  case RECEIVING:
  ^~~~

drivers/hsi/clients/ssi_protocol.c: In function ‘ssip_keep_alive’:
drivers/hsi/clients/ssi_protocol.c:466:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    if (atomic_read(&ssi->tx_usecnt) == 0)
       ^
drivers/hsi/clients/ssi_protocol.c:472:3: note: here
   case SEND_IDLE:
   ^~~~

Notice that, in this particular case, the code comment is
modified in accordance with what GCC is expecting to find.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/hsi/clients/ssi_protocol.c

@@ -290,7 +290,7 @@ static void ssip_set_rxstate(struct ssi_protocol *ssi, unsigned int state)
 		/* CMT speech workaround */
 		if (atomic_read(&ssi->tx_usecnt))
 			break;
-		/* Otherwise fall through */
+		/* Else, fall through */
 	case RECEIVING:
 		mod_timer(&ssi->keep_alive, jiffies +
 						msecs_to_jiffies(SSIP_KATOUT));
@@ -465,9 +465,10 @@ static void ssip_keep_alive(struct timer_list *t)
 		case SEND_READY:
 			if (atomic_read(&ssi->tx_usecnt) == 0)
 				break;
+			/* Fall through */
 			/*
-			 * Fall through. Workaround for cmt-speech
-			 * in that case we relay on audio timers.
+			 * Workaround for cmt-speech in that case
+			 * we relay on audio timers.
 			 */
 		case SEND_IDLE:
 			spin_unlock(&ssi->lock);