Stocks Down, Starbucks, Techs Fall  NEW YORK (Reuters) - U.S. stocks were slightly lower on  Thursday, as a broker downgrade on the semiconductor industry  rattled investors, while coffee-shop chain Starbucks &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=SBUX.O target=/stocks/quickinfo/fullquote"&gt;SBUX.O&lt;/A&gt;  disappointed with slowing growth.