tty: Add closing marker into comment in tty_ldisc.h

The closing `` is missing. Add it.

Fixes: 6bb6fa69 ("tty: Implement lookahead to process XON/XOFF timely")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/9bc6d45d-48c8-519-1646-78ba22505b1f@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>