tty: add missing const to termios hw-change helper

Add missing const qualifiers to the parameters of the termios hw-change
helper, which is used by a few USB serial drivers. This specifically
allows the pl2303 driver to use const arguments in one of its helper as
well.

Cc: Jiri Slaby <jslaby@suse.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 1dd587ba..955cd0c 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -527,7 +527,7 @@ static inline speed_t tty_get_baud_rate(struct tty_struct *tty)
 }
 
 extern void tty_termios_copy_hw(struct ktermios *new, struct ktermios *old);
-extern int tty_termios_hw_change(struct ktermios *a, struct ktermios *b);
+extern int tty_termios_hw_change(const struct ktermios *a, const struct ktermios *b);
 extern int tty_set_termios(struct tty_struct *tty, struct ktermios *kt);
 
 extern struct tty_ldisc *tty_ldisc_ref(struct tty_struct *);