ASoC: rt5645: Restore HP depop setting in HP off

This driver will set RT5645_DEPOP_MAN bit in headphone power up
depop process. We need to restore it in headphone power down
process. Otherwise, we will get headphone noise when push button
function is enabled.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>