Set environment variable QT_AUTO_SCREEN_SCALE_FACTOR in Qt 5.6.

Amends de3b2b6493 to set the
variable.

Change-Id: I305e0d911e42f76ee6f93406c012000a63bf7bc5
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@theqtcompany.com>

src/app/main.cpp

@@ -299,6 +299,8 @@ int main(int argc, char **argv)
             && !qEnvironmentVariableIsSet("QT_DEVICE_PIXEL_RATIO")) {
         qputenv("QT_DEVICE_PIXEL_RATIO", "auto");
     }
+#else
+    qputenv("QT_AUTO_SCREEN_SCALE_FACTOR", "1");
 #endif // < Qt 5.6
 
     QLoggingCategory::setFilterRules(QLatin1String("qtc.*.debug=false"));