regulator: da9121: Constify struct regmap_config

`da9121_1ch_regmap_config` and `da9121_2ch_regmap_config` are not
modified and can be declared as const to move their data to a
read-only section.

The pointer that references those structs has been converted to const
accordingly.

Signed-off-by: Javier Carrasco <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/regulator/da9121-regulator.c

···
 };
 
 /* DA9121 regmap config for 1 channel variants */
-static struct regmap_config da9121_1ch_regmap_config = {
+static const struct regmap_config da9121_1ch_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = DA9121_REG_OTP_CONFIG_ID,
···
 };
 
 /* DA9121 regmap config for 2 channel variants */
-static struct regmap_config da9121_2ch_regmap_config = {
+static const struct regmap_config da9121_2ch_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.max_register = DA9121_REG_OTP_CONFIG_ID,
···
 static int da9121_assign_chip_model(struct i2c_client *i2c,
 			struct da9121 *chip)
 {
-	struct regmap_config *regmap;
+	const struct regmap_config *regmap;
 	int ret = 0;
 
 	chip->dev = &i2c->dev;