ALSA: use linux/io.h to fix compile warnings

For helping to reduce Greert's regression list...
  src/sound/drivers/mtpav.c: error: implicit declaration of function 'inb'
  src/sound/drivers/mtpav.c: error: implicit declaration of function 'outb'
  ...

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/pcmcia/vx/vxp_ops.c b/sound/pcmcia/vx/vxp_ops.c
index 989e04a..fe33e12 100644
--- a/sound/pcmcia/vx/vxp_ops.c
+++ b/sound/pcmcia/vx/vxp_ops.c
@@ -23,8 +23,8 @@
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/firmware.h>
+#include <linux/io.h>
 #include <sound/core.h>
-#include <asm/io.h>
 #include "vxpocket.h"