ALSA: hda - Make sure mute LEDs stay on during runtime suspend (Realtek)

Some HP machines with Realtek codecs have mute LEDs connected to VREF pins.
However when these go into runtime suspend, the pin powers down and its
pin control is disabled, thus disabling the LED too.

This patch fixes that issue by making sure that the pin stays in D0 with
correct pin control.

Cc: stable@kernel.org
BugLink: https://bugs.launchpad.net/bugs/1248465
Tested-by: Franz Hsieh <franz.hsieh@canonical.com>
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>