The pnum passed to set_page_attr and test_page_attr should from
0 to storage.file_pages - 1, but bitmap_file_set_bit and
bitmap_file_clear_bit call set_page_attr and test_page_attr with
page->index parameter while page->index has already added node_offset
before.

So we need to minus node_offset in both bitmap_file_clear_bit
and bitmap_file_set_bit.
Reviewed-by: NNeilBrown <neilb@suse.com>
Signed-off-by: NGuoqing Jiang <gqjiang@suse.com>
Signed-off-by: NShaohua Li <shli@fb.com>