Turn calls to bi->bi_end_io() into bio_endio(). Apparently bio_endio does
exactly the same error processing as is hardcoded at these places.

bio_endio() avoids recursion (or will soon), so it should be used.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Neil Brown <neilb@suse.de>