With this function converted to subpage compatible sector interfaces,
the following helper functions can be removed:

- rbio_stripe_page()
- rbio_pstripe_page()
- rbio_qstripe_page()
- page_in_rbio()
Signed-off-by: NQu Wenruo <wqu@suse.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>