ASoC: max98357a: request GPIO when device get probed

devm_gpiod_get_optional() returns EBUSY after component rebound.

Request GPIO in max98357a_platform_probe() to support component
rebinding.

Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Signed-off-by: Mark Brown <broonie@kernel.org>