By Jess Jones Wall Street darling Arm is set to report fourth quarter earnings on Wednesday amid a slowdown in sales and growing concern it is overvalued. Shares in the Cambridge-based chip designer have soared 60 per cent over the past year as investors have piled in on one of the newest admissions to New York’s Nasdaq exchange. In February, Arm hammered analyst estimates for its third-quarter earnings, prompting the stock to double in three days. This was despite it reporting a slowdown in earnings and sales. Revenue rose just 14 per cent year on year to $824m (£655m), down from a 28 per cen…