mm: don't include <linux/blkdev.h> in <linux/backing-dev.h>

Move inode_to_bdi out of line to avoid having to include blkdev.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210920123328.1399408-4-hch@lst.de


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