mfd: max77686: 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 <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/max77686.c

···
 		max77802_rtc_is_volatile_reg(dev, reg));
 }
 
-static struct regmap_config max77686_regmap_config = {
+static const struct regmap_config max77686_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 };
 
-static struct regmap_config max77686_rtc_regmap_config = {
+static const struct regmap_config max77686_rtc_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 };
 
-static struct regmap_config max77802_regmap_config = {
+static const struct regmap_config max77802_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.writeable_reg = max77802_is_accessible_reg,