ASoC: Intel: kbl-rt5660: use .exit() dailink callback to release gpiod

The gpiod handling is inspired from the bdw-rt5677 code. Apply same
fix to avoid reference count issue while removing modules for
consistency.

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Reviewed-by: Curtis Malainey <curtis@malainey.com>
Link: https://lore.kernel.org/r/20200622154241.29053-4-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>