mfd: hi6421-pmic: Constify struct regmap_config

The regmap_config struct may be const because it is not modified by the
driver and regmap_init() accepts pointer to const.
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/hi6421-pmic-core.c

@@ -35,7 +35,7 @@ static const struct mfd_cell hi6421_devs[] = {
 	{ .name = "hi6421-regulator", },
 };
 
-static struct regmap_config hi6421_regmap_config = {
+static const struct regmap_config hi6421_regmap_config = {
 	.reg_bits = 32,
 	.reg_stride = 4,
 	.val_bits = 8,