f2fs: fix to return correct error number in f2fs_sync_node_pages()

If __write_node_folio() failed, it will return AOP_WRITEPAGE_ACTIVATE,
the incorrect return value may be passed to userspace in below path,
fix it.

- sync_filesystem
 - sync_fs
  - f2fs_issue_checkpoint
   - block_operations
    - f2fs_sync_node_pages
     - __write_node_folio
     : return AOP_WRITEPAGE_ACTIVATE

Cc: stable@vger.kernel.org
Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>