regmap: Make reg_config reg_defaults const

The reg_defaults field usually points to a static per driver array, which should
not be modified. Make requirement this explicit by making reg_defaults const.
To allow this the regcache_init code needs some minor changes. Previoulsy the
reg_config was not available in regcache_init and regmap->reg_defaults was used
to pass the default register set to regcache_init. Now that the reg_config is
available we can work on it directly.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index 1e4ec2b..458f15f 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -83,7 +83,7 @@
 	bool (*precious_reg)(struct device *dev, unsigned int reg);
 
 	unsigned int max_register;
-	struct reg_default *reg_defaults;
+	const struct reg_default *reg_defaults;
 	unsigned int num_reg_defaults;
 	enum regcache_type cache_type;
 	const void *reg_defaults_raw;