ASoC: wm_hubs: Bomb out if we can't read back the DC servo result

Should have no practical impact but it's safer than trying to soldier on.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/wm_hubs.c

@@ -172,7 +172,7 @@ static void calibrate_dc_servo(struct snd_soc_codec *codec)
 		break;
 	default:
 		WARN(1, "Unknown DCS readback method\n");
-		break;
+		return;
 	}
 
 	dev_dbg(codec->dev, "DCS input: %x %x\n", reg_l, reg_r);