block: ensure iov_iter advances for added pages

There are cases where a bio may not accept additional pages, and the iov
needs to advance to the last data length that was accepted. The zone
append used to handle this correctly, but was inadvertently broken when
the setup was made common with the normal r/w case.

Fixes: 576ed913 ("block: use bio_add_page in bio_iov_iter_get_pages")
Fixes: c58c0074 ("block/bio: remove duplicate append pages code")
Signed-off-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20220712153256.2202024-1-kbusch@fb.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>