ASoC: rockchip: mark OF related data as maybe unused

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

  sound/soc/rockchip/rockchip_i2s.c:569:34: warning: ‘rockchip_i2s_match’ defined but not used [-Wunused-const-variable=]
  sound/soc/rockchip/rockchip_pdm.c:463:34: warning: ‘rockchip_pdm_match’ defined but not used [-Wunused-const-variable=]
  sound/soc/rockchip/rockchip_spdif.c:44:34: warning: ‘rk_spdif_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-12-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/rockchip/rockchip_i2s.c

@@ -566,7 +566,7 @@ static const struct rk_i2s_pins rk3399_i2s_pins = {
 	.shift = 11,
 };
 
-static const struct of_device_id rockchip_i2s_match[] = {
+static const struct of_device_id rockchip_i2s_match[] __maybe_unused = {
 	{ .compatible = "rockchip,rk3066-i2s", },
 	{ .compatible = "rockchip,rk3188-i2s", },
 	{ .compatible = "rockchip,rk3288-i2s", },

sound/soc/rockchip/rockchip_pdm.c

@@ -460,7 +460,7 @@ static const struct regmap_config rockchip_pdm_regmap_config = {
 	.cache_type = REGCACHE_FLAT,
 };
 
-static const struct of_device_id rockchip_pdm_match[] = {
+static const struct of_device_id rockchip_pdm_match[] __maybe_unused = {
 	{ .compatible = "rockchip,pdm",
 	  .data = (void *)RK_PDM_RK3229 },
 	{ .compatible = "rockchip,px30-pdm",

sound/soc/rockchip/rockchip_spdif.c

@@ -41,7 +41,7 @@ struct rk_spdif_dev {
 	struct regmap *regmap;
 };
 
-static const struct of_device_id rk_spdif_match[] = {
+static const struct of_device_id rk_spdif_match[] __maybe_unused = {
 	{ .compatible = "rockchip,rk3066-spdif",
 	  .data = (void *)RK_SPDIF_RK3066 },
 	{ .compatible = "rockchip,rk3188-spdif",