dm: dm-zoned: use __bio_add_page for adding single metadata page

dm: dm-zoned: use __bio_add_page for adding single metadata page

dm-zoned uses bio_add_page() for adding a single page to a freshly created
metadata bio.

Use __bio_add_page() instead as adding a single page to a new bio is
always guaranteed to succeed.

This brings us a step closer to marking bio_add_page() __must_check

Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/55a0c8dad7550379647873b579dc7cfbe0191f96.1685532726.git.johannes.thumshirn@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>