BIOS on ASUS G751 doesn't seem to map the headphone pin (NID 0x16)
correctly.  Add a quirk to address it, as well as chaining to the
previous fix for the microphone.
Reported-by: Håvard <hovardslill@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>