ALSA: Include linux/io.h instead of asm/io.h

Nowadays it's recommended.  Replace all in a shot.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/drivers/opl4/opl4_synth.c b/sound/drivers/opl4/opl4_synth.c
index 4b91adc..7bc1e58 100644
--- a/sound/drivers/opl4/opl4_synth.c
+++ b/sound/drivers/opl4/opl4_synth.c
@@ -33,7 +33,7 @@
 
 #include "opl4_local.h"
 #include <linux/delay.h>
-#include <asm/io.h>
+#include <linux/io.h>
 #include <sound/asoundef.h>
 
 /* GM2 controllers */