serial: constify serial_assign()

Signed-off-by: Gerlando Falauto <gerlando.falauto@keymile.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/serial.h b/include/serial.h
index 9d623ca..fbc1036 100644
--- a/include/serial.h
+++ b/include/serial.h
@@ -93,7 +93,7 @@
 extern void serial_register(struct serial_device *);
 extern void serial_initialize(void);
 extern void serial_stdio_init(void);
-extern int serial_assign(char *name);
+extern int serial_assign(const char *name);
 extern void serial_reinit_all(void);
 
 /* For usbtty */