tty: update obsolete termios comment

Update an obsolete comment referring to the termios_locked structure
which was removed over a decade ago by commit fe6e29fd ("tty:
simplify ktermios allocation").

While at it, fix the "Thus" typo.
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -1173,7 +1173,7 @@ static struct tty_struct *tty_driver_lookup_tty(struct tty_driver *driver,
  *	tty_init_termios	-  helper for termios setup
  *	@tty: the tty to set up
  *
- *	Initialise the termios structures for this tty. Thus runs under
+ *	Initialise the termios structure for this tty. This runs under
  *	the tty_mutex currently so we can be relaxed about ordering.
  */