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/serial-u16550.c b/sound/drivers/serial-u16550.c
index 8c1dc73..1927b89 100644
--- a/sound/drivers/serial-u16550.c
+++ b/sound/drivers/serial-u16550.c
@@ -37,6 +37,7 @@
 #include <linux/slab.h>
 #include <linux/ioport.h>
 #include <linux/module.h>
+#include <linux/io.h>
 #include <sound/core.h>
 #include <sound/rawmidi.h>
 #include <sound/initval.h>
@@ -44,8 +45,6 @@
 #include <linux/serial_reg.h>
 #include <linux/jiffies.h>
 
-#include <asm/io.h>
-
 MODULE_DESCRIPTION("MIDI serial u16550");
 MODULE_LICENSE("GPL");
 MODULE_SUPPORTED_DEVICE("{{ALSA, MIDI serial u16550}}");