ASoC: ak4642: fixup HeadPhone L/R dapm settings

Current ak4642 driver had wrong dapm settings for headphone L/R.
If you select headphone L, and select R after that,
headphone L setting was removed by R settings.

This patch fixes it up.
It provides just "Headphone Enable" to user side

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>