ALSA: hda - Add stereo mic quirk for Lenovo G50-70 (17aa:3978)

Lenovo G50-70 (17aa:3978) with Conexant codec chip requires the
similar workaround for the inverted stereo dmic like other Lenovo
models.

Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1020657
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>