ASoC: codecs: max98390: simplify getting the adapter of a client

We have a dedicated pointer for that, so use it. Much easier to read and
less computation involved.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20210918213553.14514-2-wsa+renesas@sang-engineering.com


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