Add missing includes found using -Wmissing-declarations.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@31396 a1c6a512-1295-4272-9138-f99709370657

firmware/drivers/audio/tsc2100.c

@@ -26,6 +26,7 @@
 #include "audio.h"
 
 #include "audiohw.h"
+#include "sound.h"
 #include "tsc2100.h"
 
 const struct sound_settings_info audiohw_settings[] = {

firmware/drivers/audio/wm8751.c

@@ -30,6 +30,7 @@
 #include "audio.h"
 #include "audiohw.h"
 #include "system.h"
+#include "sound.h"
 
 const struct sound_settings_info audiohw_settings[] = {
     [SOUND_VOLUME]        = {"dB", 0,  1, -74,   6, -25},

firmware/drivers/audio/wm8758.c

@@ -31,6 +31,7 @@
 
 #include "wmcodec.h"
 #include "audiohw.h"
+#include "sound.h"
 
 const struct sound_settings_info audiohw_settings[] = {
     [SOUND_VOLUME]        = {"dB", 0,  1, -90,   6, -25},

firmware/drivers/audio/wm8978.c

@@ -27,6 +27,7 @@
 #include "audio.h"
 /*#define LOGF_ENABLE*/
 #include "logf.h"
+#include "sound.h"
 
 /* TODO: Define/refine an API for special hardware steps outside the
  * main codec driver such as special GPIO handling. */