[docs] Update HTML pages to refer to CSS in a way that works locally and with Sphinx.

llvm-svn: 155153
diff --git a/llvm/docs/LangRef.html b/llvm/docs/LangRef.html
index 9989cc8..cdf2807 100644
--- a/llvm/docs/LangRef.html
+++ b/llvm/docs/LangRef.html
@@ -7,7 +7,7 @@
   <meta name="author" content="Chris Lattner">
   <meta name="description"
   content="LLVM Assembly Language Reference Manual.">
-  <link rel="stylesheet" href="llvm.css" type="text/css">
+  <link rel="stylesheet" href="_static/llvm.css" type="text/css">
 </head>
 
 <body>