Analysis: Fix example usage comment in CFG.cpp. NFC

Patch by Vedant Kumar!

llvm-svn: 243275

clang/lib/Analysis/CFG.cpp

@@ -284,7 +284,7 @@ reverse_children::reverse_children(Stmt *S) {
 ///   Example usage:
 ///
 ///     CFGBuilder builder;
-///     CFG* cfg = builder.BuildAST(stmt1);
+///     std::unique_ptr<CFG> cfg = builder.buildCFG(decl, stmt1);
 ///
 ///  CFG construction is done via a recursive walk of an AST.  We actually parse
 ///  the AST in reverse order so that the successor of a basic block is