ASoC: sgtl5000: Fix setting mic bias resistor

According to the datasheet:
CHIP_MIC_CTRL 0x002A

BITS[9:8] BIAS_RESISTOR
        0x0 = Powerd off
        0x1 = 2.0 kohm
        0x2 = 4.0 kohm
        0x3 = 8.0 kohm

To set mic bias resistor, we need to update bits[9:8] of
SGTL5000_CHIP_MIC_CTRL register.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/sgtl5000.c

@@ -131,16 +131,13 @@ static int mic_bias_event(struct snd_soc_dapm_widget *w,
 	case SND_SOC_DAPM_POST_PMU:
 		/* change mic bias resistor to 4Kohm */
 		snd_soc_update_bits(w->codec, SGTL5000_CHIP_MIC_CTRL,
-				SGTL5000_BIAS_R_4k, SGTL5000_BIAS_R_4k);
+				SGTL5000_BIAS_R_MASK,
+				SGTL5000_BIAS_R_4k << SGTL5000_BIAS_R_SHIFT);
 		break;
 
 	case SND_SOC_DAPM_PRE_PMD:
-		/*
-		 * SGTL5000_BIAS_R_8k as mask to clean the two bits
-		 * of mic bias and output impedance
-		 */
 		snd_soc_update_bits(w->codec, SGTL5000_CHIP_MIC_CTRL,
-				SGTL5000_BIAS_R_8k, 0);
+				SGTL5000_BIAS_R_MASK, 0);
 		break;
 	}
 	return 0;