[mtpresponder] Cleanup -Wimplicit-fallthrough warnings

Build uses -Wextra, which implies -Wimplicit-fallthrough=3, which
is picky enough not to accept 'fall through' as intentionality hint
and leads to compilation time warnings.

Use "FALLTHRU" which is ok for all implicit-fallthrough levels that
accept comments in addition to attributes.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

mts/platform/storage/fsstorageplugin/fsstorageplugin.cpp

@@ -1,7 +1,8 @@
 /*
 * This file is part of libmeegomtp package
 *
-* Copyright (C) 2010 Nokia Corporation. All rights reserved.
+* Copyright (c) 2010 Nokia Corporation. All rights reserved.
+* Copyright (c) 2013 - 2020 Jolla Ltd.
 * Copyright (c) 2020 Open Mobile Platform LLC.
 *
 * Contact: Deepak Kodihalli <deepak.kodihalli@nokia.com>
@@ -224,6 +225,7 @@ static time_t datetime_to_time_t(const char *dt)
 
     case '-':
         east = false;
+        /* FALLTHRU */
     case '+':
         /* Localtime + utc offset */
         ++pos;

mts/protocol/mtpresponder.cpp

@@ -1,7 +1,9 @@
 /*
 * This file is part of libmeegomtp package
 *
-* Copyright (C) 2010 Nokia Corporation. All rights reserved.
+* Copyright (c) 2010 Nokia Corporation. All rights reserved.
+* Copyright (c) 2013 - 2020 Jolla Ltd.
+* Copyright (c) 2020 Open Mobile Platform LLC.
 *
 * Contact: Santosh Puranik <santosh.puranik@nokia.com>
 *
@@ -3098,7 +3100,7 @@ void MTPResponder::dispatchEvent(MTPEventCode event, const QVector<quint32> &par
     switch( event ) {
     case MTP_EV_ObjectAdded:
         filteringAllowed = false;
-        // fall throught
+        // FALLTHRU
     case MTP_EV_ObjectRemoved:
     case MTP_EV_ObjectInfoChanged:
     case MTP_EV_ObjectPropChanged: