ASoC: adau1977: Fix reset-gpios typo

This change fixes a typo in the dt-binding examples (reset_gpio ->
reset-gpios).
Even though 'reset-gpio' is a valid construct for gpiolib the naming
'reset-gpios' is more suited for dt-bindings documentation.

Signed-off-by: Bogdan Togorean <bogdan.togorean@analog.com>
Signed-off-by: Mark Brown <broonie@kernel.org>