ASoC: rt5645: make RT5650_TDM_CTRL_4 readable

Register RT5650_TDM_CTRL_4(0x7A) is readable and used for mixer
setting. It should be added in rt5645_readable_register function.
Signed-off-by: NBard Liao <bardliao@realtek.com>
Signed-off-by: NOder Chiou <oder_chiou@realtek.com>
Signed-off-by: NMark Brown <broonie@kernel.org>

sound/soc/codecs/rt5645.c

@@ -349,6 +349,7 @@ static bool rt5645_readable_register(struct device *dev, unsigned int reg)
 	case RT5645_TDM_CTRL_1:
 	case RT5645_TDM_CTRL_2:
 	case RT5645_TDM_CTRL_3:
+	case RT5650_TDM_CTRL_4:
 	case RT5645_GLB_CLK:
 	case RT5645_PLL_CTRL1:
 	case RT5645_PLL_CTRL2: