tty: serial: mux: include <linux/io.h> instead of <asm/io.h>

Include the more general linux/io.h instead of asm/io.h
as checkpatch suggests.

Signed-off-by: Zihao Tang <[e-mail]>
Signed-off-by: Jay Fang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/mux.c

···
 #include <linux/console.h>
 #include <linux/delay.h> /* for udelay */
 #include <linux/device.h>
-#include <asm/io.h>
+#include <linux/io.h>
 #include <asm/irq.h>
 #include <asm/parisc-device.h>