ASoC: mt8192: Report an error if when an invalid sidetone gain is written

Reporting an error on invalid values is optional but helpful to userspace
so do so.

Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230223-asoc-mt8192-quick-fixes-v1-3-9a85f90368e1@kernel.org


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