block: remove bio_clone() and all references.

bio_clone() is no longer used.
Only bio_clone_bioset() or bio_clone_fast().
This is for the best, as bio_clone() used fs_bio_set,
and filesystems are unlikely to want to use bio_clone().

So remove bio_clone() and all references.
This includes a fix to some incorrect documentation.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-merge.c

@@ -115,13 +115,13 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 		 * With arbitrary bio size, the incoming bio may be very
 		 * big. We have to split the bio into small bios so that
 		 * each holds at most BIO_MAX_PAGES bvecs because
-		 * bio_clone() can fail to allocate big bvecs.
+		 * bio_clone_bioset() can fail to allocate big bvecs.
 		 *
-		 * Those drivers which will need to use bio_clone()
+		 * Those drivers which will need to use bio_clone_bioset()
 		 * should tell us in some way.  For now, impose the
 		 * BIO_MAX_PAGES limit on all queues.
 		 *
-		 * TODO: handle users of bio_clone() differently.
+		 * TODO: handle users of bio_clone_bioset() differently.
 		 */
 		if (bvecs++ >= BIO_MAX_PAGES)
 			goto split;