ASoC: Intel: bdw-rt5677: Use devm_gpiod_get()

Since index is always 0 replace devm_gpiod_get_index() by devm_gpiod_get()
and apply proper flags.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>