block: bio_remaining_done() isn't unlikely

We use bio chaining during most I/Os these days due to the delayed
bio splitting.  Additionally XFS will start using it, and there is
a pending direct I/O rewrite also making heavy use for it.  Don't
pretend it's always unlikely, and let the branch predictor do it's
job instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>