ASoC: rt5645: Mark RT5645_TDM_CTRL_3 as readable

amixer query fails due to it is not readable reigster

Signed-off-by: Fang, Yang A <yang.a.fang@intel.com>
Acked-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>