block: use page_to_phys in bvec_phys

Use page_to_phys instead of open coding it now that it is available in an
architecture independent way.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250106081437.798213-1-hch@lst.de


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