ledc_update_duty() function

- ESP_OK Success - ESP_ERR_INVALID_ARG Parameter error

Call this function to activate the LEDC updated parameters. After ledc_set_duty, we need to call this function to update the settings. And the new LEDC parameters don't take effect until the next PWM cycle. ledc_set_duty, ledc_set_duty_with_hpoint and ledc_update_duty are not thread-safe, do not call these functions to control one LEDC channel in different tasks at the same time. A thread-safe version of API is ledc_set_duty_and_update If `CONFIG_LEDC_CTRL_FUNC_IN_IRAM` is enabled, this function will be placed in the IRAM by linker, makes it possible to execute even when the Cache is disabled. This function is allowed to run within ISR context.