Asset Sales Seen of Limited Use to US Air  CHICAGO (Reuters) - US Airways Group Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=UAIR.O target=/stocks/quickinfo/fullquote"&gt;UAIR.O&lt;/A&gt;,  desperately trying to slash costs in bankruptcy to ensure  survival, may not be able to find much relief through a  potential sale of its assets, analysts said on Tuesday.