sound: Remove some forward declarations from sound.h and uaudio.h

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

sys/dev/sound/pcm/sound.h

@@ -75,15 +75,12 @@
 #include <sys/mutex.h>
 #include <sys/condvar.h>
 
-struct pcm_channel;
-struct pcm_feeder;
-struct snd_dbuf;
 struct snd_mixer;
 
-#include <dev/sound/pcm/buffer.h>
 #include <dev/sound/pcm/matrix.h>
 #include <dev/sound/pcm/channel.h>
 #include <dev/sound/pcm/feeder.h>
+#include <dev/sound/pcm/buffer.h>
 #include <dev/sound/pcm/mixer.h>
 #include <dev/sound/pcm/dsp.h>
 

sys/dev/sound/usb/uaudio.h

@@ -33,9 +33,7 @@
 
 struct uaudio_chan;
 struct uaudio_softc;
-struct snd_dbuf;
 struct snd_mixer;
-struct pcm_channel;
 
 extern int	uaudio_attach_sub(device_t dev, kobj_class_t mixer_class,
 		    kobj_class_t chan_class);