Fix checkwps build for dx50 & dx90 targets

Their codec headers weren't in the right place.

Change-Id: Iae16c10defc937cc227afd8992ff45cd6d664898

firmware/export/codec-dx90.h

@@ -0,0 +1,35 @@
+/***************************************************************************
+ *             __________               __   ___
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ *
+ * Copyright (C) 2014 by Ilia Sergachev: Initial Rockbox port to iBasso DX50
+ * Copyright (C) 2014 by Mario Basister: iBasso DX90 port
+ * Copyright (C) 2014 by Simon Rothen: Initial Rockbox repository submission, additional features
+ * Copyright (C) 2014 by Udo Schläpfer: Code clean up, additional features
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+
+#ifndef _CODEC_DX90_H_
+#define _CODEC_DX90_H_
+
+
+#define AUDIOHW_CAPS MONO_VOL_CAP
+
+
+AUDIOHW_SETTING(VOLUME, "", 0, 1, -255, 0, -128)
+
+
+#endif