ASoC: tlv320aic3x: Use gpio_is_valid in checking for valid gpio_reset

I promised to convert this at some point.

Signed-off-by: Jarkko Nikula <jhnikula@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>