sound: Merge PCM_ALIVE() with PCM_REGISTERED()

PCM_ALIVE() is used only in pcm_unregister(), but it does not hurt to
use PCM_REGISTERED(), which uses PCM_ALIVE() internally. In fact, it's
more robust this way.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

sys/dev/sound/pcm/sound.c

@@ -467,7 +467,7 @@ pcm_unregister(device_t dev)
 
 	d = device_get_softc(dev);
 
-	if (!PCM_ALIVE(d)) {
+	if (!PCM_REGISTERED(d)) {
 		device_printf(dev, "unregister: device not configured\n");
 		return (0);
 	}

sys/dev/sound/pcm/sound.h

@@ -133,8 +133,8 @@ struct snd_mixer;
 				"\015PVCHANS"				\
 				"\016RVCHANS"
 
-#define PCM_ALIVE(x)		((x) != NULL && (x)->lock != NULL)
-#define PCM_REGISTERED(x)	(PCM_ALIVE(x) && ((x)->flags & SD_F_REGISTERED))
+#define PCM_REGISTERED(x)	\
+	((x) != NULL && (x)->lock != NULL && ((x)->flags & SD_F_REGISTERED))
 
 #define	PCM_MAXCHANS		10000
 #define	PCM_CHANCOUNT(d)	\