ASoC: rt5682: Remove HP volume control

This patch removed Headphone Playback Volume control.
Due to codec settings, we don't want the user to change HP analog gain.
The user could use DAC1 Playback Volume control to
change playback volume.

Signed-off-by: Shuming Fan <shumingf@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>