hwmon: (max1668) Add missing dependency on REGMAP_I2C

This driver requires REGMAP_I2C to be selected in order to get access to
regmap_config, regmap_bus, and devm_regmap_init_i2c.
Add the missing dependency.

Fixes: 021730ac ("hwmon: (max1668) Convert to use regmap")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Message-ID: <20241002-hwmon-select-regmap-v1-4-548d03268934@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>