tty: Add closing marker into comment in tty_ldisc.h

The closing `` is missing. Add it.

Fixes: 6bb6fa6 ("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>

include/linux/tty_ldisc.h

@@ -187,7 +187,7 @@ int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
  *	function for automatic flow control.
  *
  * @lookahead_buf: [DRV] ``void ()(struct tty_struct *tty,
- *			const unsigned char *cp, const char *fp, int count)
+ *			const unsigned char *cp, const char *fp, int count)``
  *
  *	This function is called by the low-level tty driver for characters
  *	not eaten by ->receive_buf() or ->receive_buf2(). It is useful for