ASoC: es7241: mark OF related data as maybe unused

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

  sound/soc/codecs/es7241.c:206:33: warning: ‘es7241_chip’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-35-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/es7241.c

@@ -203,7 +203,7 @@ static const struct es7241_clock_mode es7241_modes[] = {
 	},
 };
 
-static const struct es7241_chip es7241_chip = {
+static const struct es7241_chip es7241_chip __maybe_unused = {
 	.modes = es7241_modes,
 	.mode_num = ARRAY_SIZE(es7241_modes),
 };