[Ada] Simplify repeated calls in printing of GNAT AST

[Pierre-Marie de Rodat via Gcc-patches]

Code cleanup; behaviour is unaffected.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

        * treepr.adb (Visit_Node): Simplify repeated call to
        Next_Entity.
diff --git a/gcc/ada/treepr.adb b/gcc/ada/treepr.adb
--- a/gcc/ada/treepr.adb
+++ b/gcc/ada/treepr.adb
@@ -2305,8 +2305,8 @@ package body Treepr is
             begin
                Nod := N;
                while Present (Nod) loop
-                  Visit_Descendant (Union_Id (Next_Entity (Nod)));
                   Next_Entity (Nod);
+                  Visit_Descendant (Union_Id (Nod));
                end loop;
             end;
          end if;