Add const to dp/dmic snd_soc_ops.

Fixes: 626d84db (ASoC: rockchip: Add support for DMIC codec)
Fixes: 3313faf1 (ASoC: rockchip: Add support for DP codec)
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>