The closing `` is missing. Add it.

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