f2fs: don't change wbc->sync_mode

We should never falsify wbc->sync_mode passed from mm, otherwise
mm can trigger writeback with wrong IO priority.
Signed-off-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.c

@@ -1741,7 +1741,6 @@ static int f2fs_write_node_pages(struct address_space *mapping,
 	trace_f2fs_writepages(mapping->host, wbc, NODE);
 
 	diff = nr_pages_to_write(sbi, NODE, wbc);
-	wbc->sync_mode = WB_SYNC_NONE;
 	blk_start_plug(&plug);
 	f2fs_sync_node_pages(sbi, wbc, true, FS_NODE_IO);
 	blk_finish_plug(&plug);