ASoC: max98373: don't access volatile registers in bias level off

ASoC: max98373: don't access volatile registers in bias level off

We will set regcache_cache_only true in suspend. As a result,
regmap_read will return error when we try to read volatile
registers in suspend. Besides, it doesn't make sense to read
feedback data when codec is not active. To make userspace
happy, this patch returns a cached value shich should be a
valid value.

Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20201217074556.32370-1-yung-chuan.liao@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>