Last month, WK Kellogg CEO Gary Pilnick faced online backlash after suggesting that budget-conscious consumers could eat cereal for dinner in order to save money. Now, the food company is under fire yet again over the ingredients in its cereals—and the complaints are coming from one of its own investors. Jason Karp, a Kellogg shareholder and founder of the healthy foods company HumanCo, sent a letter to the company on March 13 to call it out for…