ASoC: Enable WM8990 ADC clocking workaround

Enable a hardware workaround which avoids problems with the clocking of
the ADCs in certain configurations.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/sound/soc/codecs/wm8990.c b/sound/soc/codecs/wm8990.c
index 5c84f02..938e154 100644
--- a/sound/soc/codecs/wm8990.c
+++ b/sound/soc/codecs/wm8990.c
@@ -1272,9 +1272,11 @@
 
 			/* disable POBCTRL, SOFT_ST and BUFDCOPEN */
 			wm8990_write(codec, WM8990_ANTIPOP2, WM8990_BUFIOEN);
-		} else {
-			/* ON -> standby */
 
+			/* Enable workaround for ADC clocking issue. */
+			wm8990_write(codec, WM8990_EXT_ACCESS_ENA, 0x2);
+			wm8990_write(codec, WM8990_EXT_CTL1, 0xa003);
+			wm8990_write(codec, WM8990_EXT_ACCESS_ENA, 0);
 		}
 		break;