Wall Street Seen Flat; TI Buyback to Buoy  LONDON (Reuters) - U.S. stocks were set for a steady start  on Friday with a billion dollar share buyback plan at Texas  Instruments &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=TXN.N target=/stocks/quickinfo/fullquote"&gt;TXN.N&lt;/A&gt; lending some backbone to the technology  sector.