sdktool: Mark fallthrough cases correctly

after f4d30a6798

Change-Id: Ic5ac727fa9cb2c097372c404a06e9f2a16d3f016
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/tools/sdktool/addvalueoperation.cpp

@@ -63,8 +63,10 @@ bool AddValueOperation::setArguments(const QStringList &args)
         switch (args.size()) {
         case 0:
             std::cerr << " file,";
+            Q_FALLTHROUGH();
         case 1:
             std::cerr << " key and";
+            Q_FALLTHROUGH();
         case 2:
             std::cerr << " values";
             break;