pvcalls-front: fixes incorrect error handling

kfree() is incorrectly used to release the pages allocated by
__get_free_page() and __get_free_pages(). Use the matching deallocators
i.e., free_page() and free_pages(), respectively.

Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 2f11ca7..77224d8 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -385,8 +385,8 @@
 out_error:
 	if (*evtchn >= 0)
 		xenbus_free_evtchn(pvcalls_front_dev, *evtchn);
-	kfree(map->active.data.in);
-	kfree(map->active.ring);
+	free_pages((unsigned long)map->active.data.in, PVCALLS_RING_ORDER);
+	free_page((unsigned long)map->active.ring);
 	return ret;
 }