tty: serial: txx9: 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/serial_txx9.c

···
 #include <linux/tty.h>
 #include <linux/tty_flip.h>
 
-#include <asm/io.h>
+#include <linux/io.h>
 
 static char *serial_version = "1.11";
 static char *serial_name = "TX39/49 Serial driver";