bsg: setting rq->bio to NULL

Due to commit 1cd96c24 ("block: WARN
in __blk_put_request() for potential bio leak"), BSG SMP requests get
the false warnings:

WARNING: at block/blk-core.c:1068 __blk_put_request+0x52/0xc0()

This sets rq->bio to NULL to avoid that false warnings.
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

block/bsg.c

@@ -315,6 +315,7 @@ bsg_map_hdr(struct bsg_device *bd, struct sg_io_v4 *hdr, fmode_t has_write_perm,
 	blk_put_request(rq);
 	if (next_rq) {
 		blk_rq_unmap_user(next_rq->bio);
+		next_rq->bio = NULL;
 		blk_put_request(next_rq);
 	}
 	return ERR_PTR(ret);
@@ -448,6 +449,7 @@ static int blk_complete_sgv4_hdr_rq(struct request *rq, struct sg_io_v4 *hdr,
 		hdr->dout_resid = rq->data_len;
 		hdr->din_resid = rq->next_rq->data_len;
 		blk_rq_unmap_user(bidi_bio);
+		rq->next_rq->bio = NULL;
 		blk_put_request(rq->next_rq);
 	} else if (rq_data_dir(rq) == READ)
 		hdr->din_resid = rq->data_len;
@@ -466,6 +468,7 @@ static int blk_complete_sgv4_hdr_rq(struct request *rq, struct sg_io_v4 *hdr,
 	blk_rq_unmap_user(bio);
 	if (rq->cmd != rq->__cmd)
 		kfree(rq->cmd);
+	rq->bio = NULL;
 	blk_put_request(rq);
 
 	return ret;