ASoC: Use BIAS_OFF when idle for wm_hubs devices

This provides a small power saving when audio is inactive.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>

sound/soc/codecs/wm_hubs.c

@@ -753,6 +753,12 @@ int wm_hubs_handle_analogue_pdata(struct snd_soc_codec *codec,
 				    WM8993_LINEOUT2_MODE,
 				    WM8993_LINEOUT2_MODE);
 
+	/* If the line outputs are differential then we aren't presenting
+	 * VMID as an output and can disable it.
+	 */
+	if (lineout1_diff && lineout2_diff)
+		codec->idle_bias_off = 1;
+
 	if (lineout1fb)
 		snd_soc_update_bits(codec, WM8993_ADDITIONAL_CONTROL,
 				    WM8993_LINEOUT1_FB, WM8993_LINEOUT1_FB);