removed findRootNode and replaced it with node.getRootNode

Author: Kolpa

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/util/PFunctionArgsFinder.java

@@ -20,18 +20,10 @@ public class PFunctionArgsFinder {
     private final RootNode rootNode;
 
     public PFunctionArgsFinder(Node node) {
-        this.rootNode = findRootNode(node);
+        this.rootNode = node.getRootNode();
         assert rootNode instanceof PRootNode;
     }
 
-    private static RootNode findRootNode(Node node) {
-        Node n = node;
-        while (!(n instanceof RootNode) && (n != null)) {
-            n = n.getParent();
-        }
-        return (RootNode) n;
-    }
-
     public ArgumentListObject collectArgs() {
         List<String> arguments = new LinkedList<>();