regulator: max77857: Constify struct regmap_config

`max77857_remgap_config` is not modified and can be declared as const to
move its data to a read-only section.
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20240704-regulator-const-regmap-v1-2-bce0ddef63ea@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/max77857-regulator.c

@@ -67,7 +67,7 @@ static bool max77857_volatile_reg(struct device *dev, unsigned int reg)
 	}
 }
 
-static struct regmap_config max77857_regmap_config = {
+static const struct regmap_config max77857_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.cache_type = REGCACHE_MAPLE,