ALSA: hda: STAC_HP_M4

Set the third microphone to a default config of a 'Line In' to be
added the Input Source Mux's.

Signed-off-by: Matthew Ranostay <mranostay@embeddedalley.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>