f2fs: use set_page_private marcro in f2fs_trace_pid

Use set_page_private marcro instead of operte page struct
directly

Signed-off-by: Yunlei He <heyunlei@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/trace.c

@@ -59,7 +59,7 @@ void f2fs_trace_pid(struct page *page)
 	pid_t pid = task_pid_nr(current);
 	void *p;
 
-	page->private = pid;
+	set_page_private(page, (unsigned long)pid);
 
 	if (radix_tree_preload(GFP_NOFS))
 		return;