ALSA: hda/realtek - Remove GPIO_MASK

GPIO_MASK was introduced in commit "df694daa [ALSA] hda-codec - Add
the support of ALC262,ALC883,ALC885,ALC861" but it's not being used. So
we can simply remove it.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>