qcacmn: Fix implicit-fallthrough compile error casued by gcc 9.3

Compiling with gcc 9.3 will cause many implicit-fallthrough
compile errors.

Fix is to add keyword fallthrough to resolve such compile error.

Change-Id: I2e7dd1525861d951e3be44f6665e149499f0f5d6
CRs-Fixed: 2785178

umac/scan/core/src/wlan_scan_filter.c

@@ -504,7 +504,8 @@ static bool scm_is_security_match(struct scan_filter *filter,
 			match = scm_check_open(filter, db_entry, security);
 			if (match)
 				break;
-		/* If not OPEN, then check WEP match so fall through */
+		/* If not OPEN, then check WEP match */
+		/* fallthrough */
 		case WLAN_CRYPTO_AUTH_SHARED:
 			match = scm_check_wep(filter, db_entry, security);
 			break;

umac/scan/core/src/wlan_scan_manager.c

@@ -1804,7 +1804,8 @@ scm_scan_event_handler(struct scheduler_msg *msg)
 	case SCAN_EVENT_TYPE_COMPLETED:
 		if (event->reason == SCAN_REASON_COMPLETED)
 			scm_11d_decide_country_code(vdev);
-		/* fall through to release the command */
+		/* release the command */
+		/* fallthrough */
 	case SCAN_EVENT_TYPE_START_FAILED:
 	case SCAN_EVENT_TYPE_DEQUEUED:
 		scm_release_serialization_command(vdev, event->scan_id);