ASoC: Intel: bytcr_rt5640: Fix Acer Iconia 8 over-current detect threshold

Change the over-current detect threshold on the Acer Iconia 8 from
2000ua to 1500uA, this fixes headset button presses not being detected.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>