ALSA: hda/realtek - Add support for Acer Aspire E5-475 headset mic

The Acer laptop Aspire E5-475 with ALC255 can't detect the headset
microphone until we modify a pin definition.

Signed-off-by: Chris Chiu <chiu@endlessm.com>
Signed-off-by: Daniel Drake <drake@endlessm.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>