ALSA: hda/realtek - Set pcbeep amp for ALC668

commit 9ad54547cf6f4410eba83bb95dfd2a0966718d6d upstream.

Set the missing pcbeep default amp for ALC668.

Signed-off-by: Kailang Yang <kailang@realtek.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>