ASoC: Support second DC servo readback method for wm_hubs

More recent Wolfson hubs devices add the ability to read back the DC
servo calibration information from the register used to write offsets,
and later still ones remove the old readback registers. Add support
for the new scheme, and use it for WM8994 device revisions that
support it.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
diff --git a/sound/soc/codecs/wm8994.c b/sound/soc/codecs/wm8994.c
index d10d651..c80218f 100644
--- a/sound/soc/codecs/wm8994.c
+++ b/sound/soc/codecs/wm8994.c
@@ -3730,11 +3730,12 @@
 	case 3:
 		wm8994->hubs.dcs_codes = -5;
 		wm8994->hubs.hp_startup_mode = 1;
+		wm8994->hubs.dcs_readback_mode = 1;
 		break;
 	default:
+		wm8994->hubs.dcs_readback_mode = 1;
 		break;
 	}
-			   
 
 	/* Remember if AIFnLRCLK is configured as a GPIO.  This should be
 	 * configured on init - if a system wants to do this dynamically