ASoC: wm8904: fix regcache handling

The current code assumes that the power is turned off in
SND_SOC_BIAS_OFF. If there are no actual regulator the codec isn't
turned off and the registers are not reset to their default values but
the regcache is still marked as dirty. Thus a value might not be written
to the hardware if it is set to the default value. Do a software reset
before turning off the power to make sure the registers are always reset
to their default states.

Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20191112223629.21867-1-michael@walle.cc
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm8904.c

@@ -1917,6 +1917,7 @@ static int wm8904_set_bias_level(struct snd_soc_component *component,
 		snd_soc_component_update_bits(component, WM8904_BIAS_CONTROL_0,
 				    WM8904_BIAS_ENA, 0);
 
+		snd_soc_component_write(component, WM8904_SW_RESET_AND_ID, 0);
 		regcache_cache_only(wm8904->regmap, true);
 		regcache_mark_dirty(wm8904->regmap);