binder: free the shrinker when binder_init() fails

binder_init() registers the shrinker before init_binderfs(). On failure
the error path returns without binder_alloc_shrinker_exit(), and a failed
module init never runs binder_exit(). The module text is freed while the
shrinker stays registered.

Mainline fixed this in adb9743d6a08 ("binder: fix memory leak in
binder_init()"). Call the existing exit helper on
err_alloc_device_names_failed, which is only reached after a successful
shrinker init.

binder/binder.c

@@ -6271,6 +6271,7 @@ err_init_binder_device_failed:
 
 err_alloc_device_names_failed:
 	debugfs_remove_recursive(binder_debugfs_dir_entry_root);
+	binder_alloc_shrinker_exit();
 
 	return ret;
 }