block: support adding less than len in bio_add_hw_page

bio_add_hw_page currently always fails or succeeds. This is fine for
the existing callers that always add PAGE_SIZE worth given that the
max_segment_size and max_sectors must always allow at least a page
worth of data. But when we want to add it for bigger amounts of data
this means it can also fail when adding the data to a bio, and creating
a fallback for that becomes really annoying in the callers.

Make use of the existing API design that allows to return a smaller
length than the one passed in and add up to max_segment_size worth
of data from a larger input. All the existing callers are fine with
this - not because they handle this return correctly, but because they
never pass more than a page in.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20231204173419.782378-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>