tty: Documentation: fix a path in a DocBook template

A wrong path to a driver breaks DocBook built.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>