block: turn macro helpers into inline functions

Replace bio_set_dev() with an identical inline helper and move it
further to fix a dependency problem with bio_associate_blkg(). Do the
same for bio_copy_dev().

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>