[POWERPC] sound: Constify & voidify get_property()

Now that get_property() returns a void *, there's no need to cast its
return value. Also, treat the return value as const, so we can
constify get_property later.

powerpc-specific sound driver changes.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

sound/aoa/core/snd-aoa-gpio-feature.c

@@ -56,7 +56,7 @@ static struct device_node *get_gpio(char *name,
 {
 	struct device_node *np, *gpio;
 	u32 *reg;
-	char *audio_gpio;
+	const char *audio_gpio;
 
 	*gpioptr = -1;