ASoC: rockchip: mark OF related data as maybe unused

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