ALSA: hda/realtek: Add Lenovo L460 to docking unit fixup

This solves the issue that a headphone is not working on the docking
unit.

Signed-off-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>