ASoC: kirkwood: armada-370-db: mark OF related data as maybe unused

The driver can be compile tested with !CONFIG_OF making certain data
unused:

  sound/soc/kirkwood/armada-370-db.c:137:34: warning: ‘a370db_dt_ids’ defined but not used [-Wunused-const-variable=]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-8-krzk@kernel.org


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