block: fix blk_rq_append_bio

Commit caa4b02476e3(blk-map: call blk_queue_bounce from blk_rq_append_bio)
moves blk_queue_bounce() into blk_rq_append_bio(), but don't consider
the fact that the bounced bio becomes invisible to caller since the
parameter type is 'struct bio *'. Make it a pointer to a pointer to
a bio, so the caller sees the right bio also after a bounce.

Fixes: caa4b02476 ("blk-map: call blk_queue_bounce from blk_rq_append_bio")
Cc: Christoph Hellwig <hch@lst.de>
Reported-by: Michele Ballabio <barra_cuda@katamail.com>
(handling failure of blk_rq_append_bio(), only call bio_get() after
blk_rq_append_bio() returns OK)
Tested-by: Michele Ballabio <barra_cuda@katamail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/osd/osd_initiator.c

@@ -1576,7 +1576,9 @@ static struct request *_make_request(struct request_queue *q, bool has_write,
 		return req;
 
 	for_each_bio(bio) {
-		ret = blk_rq_append_bio(req, bio);
+		struct bio *bounce_bio = bio;
+
+		ret = blk_rq_append_bio(req, &bounce_bio);
 		if (ret)
 			return ERR_PTR(ret);
 	}