ASoC: es7134: mark OF related data as maybe unused

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

  sound/soc/codecs/es7134.c:264:33: warning: ‘es7154_chip’ defined but not used [-Wunused-const-variable=]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-34-krzk@kernel.org


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