tty: stop using ndash in kernel-doc

An ndash used instead of a single dash renders a bullet to the result.
So use only single dashes in kernel-doc.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20230919085156.1578-11-jirislaby@kernel.org


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