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/wm8900.c

@@ -139,7 +139,6 @@
 
 struct wm8900_priv {
 	enum snd_soc_control_type control_type;
-	u16 reg_cache[WM8900_MAXREG];
 
 	u32 fll_in; /* FLL input frequency */
 	u32 fll_out; /* FLL output frequency */