ASoC: max98390: Update regmap readable reg and volatile

 Update max98390_readable_register and max98390_volatile_reg

Signed-off-by: Steve Lee <steves.lee@maximintegrated.com>
Link: https://lore.kernel.org/r/20200611094800.18422-1-steves.lee@maximintegrated.com


Signed-off-by: Mark Brown <broonie@kernel.org>