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>

sound/drivers/opl4/opl4_lib.c

@@ -23,7 +23,7 @@
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/module.h>
-#include <asm/io.h>
+#include <linux/io.h>
 
 MODULE_AUTHOR("Clemens Ladisch <clemens@ladisch.de>");
 MODULE_DESCRIPTION("OPL4 driver");