block: always use I_BDEV on file->f_mapping->host to find the bdev

Always use I_BDEV(file->f_mapping->host) to find the bdev for a file to
free up file->private_data for other uses.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230608110258.189493-29-hch@lst.de


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