cast unused return to void

should solve the warning of unused return value.

xdu.c

@@ -730,10 +730,10 @@ void printpath(int x, int y)
     np = findnode(&top, x, y);
     if (np == NULL)
         return;
-    asprintf(&path, "%s", np->name);
+    (void) asprintf(&path, "%s", np->name);
     while (np->parent != NULL) {
         tmp_path = path;
-        asprintf(&path, "%s/%s", np->parent->name, path);
+        (void) asprintf(&path, "%s/%s", np->parent->name, path);
         np = np->parent;
         free(tmp_path);
     }