mfd: Include <linux/io.h> instead of <asm/io.h>

As warned by checkpatch.pl, use #include <linux/io.h> instead of <asm/io.h>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

drivers/mfd/sm501.c

@@ -26,7 +26,7 @@
 #include <linux/sm501-regs.h>
 #include <linux/serial_8250.h>
 
-#include <asm/io.h>
+#include <linux/io.h>
 
 struct sm501_device {
 	struct list_head		list;