ASoC: Include WM8350 register definitions in CODEC header

It's expected behaviour for the CODEC header to provide them but the
WM8350 doesn't due to having all the registers together under drivers/mfd.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/wm8350.h

@@ -13,6 +13,7 @@
 #define _WM8350_H
 
 #include <sound/soc.h>
+#include <linux/mfd/wm8350/audio.h>
 
 extern struct snd_soc_dai wm8350_dai;
 extern struct snd_soc_codec_device soc_codec_dev_wm8350;