ASoC: codecs: Remove unused reg_cache fields from device structs

The multi-component patch(commit f0fba2ad1) moved the allocation of the
register cache from the driver to the ASoC core. Most drivers where adjusted to
this, but there are quite a few drivers left which now have an unused reg_cache field in
their private device struct.
This patch removes these unused fields.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/codecs/ak4671.c

@@ -27,7 +27,6 @@
 struct ak4671_priv {
 	enum snd_soc_control_type control_type;
 	void *control_data;
-	u8 reg_cache[AK4671_CACHEREGNUM];
 };
 
 /* ak4671 register cache & default register settings */