block: rename bio bi_rw to bi_opf

Since commit 63a4cc24867d, bio->bi_rw contains flags in the lower
portion and the op code in the higher portions. This means that
old code that relies on manually setting bi_rw is most likely
going to be broken. Instead of letting that brokeness linger,
rename the member, to force old and out-of-tree code to break
at compile time instead of at runtime.

No intended functional changes in this commit.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index 9393bc7..90fa4ac 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -1157,7 +1157,7 @@
 
 	bio_reset(pkt->bio);
 	pkt->bio->bi_bdev = pd->bdev;
-	pkt->bio->bi_rw = REQ_WRITE;
+	bio_set_op_attrs(pkt->bio, REQ_OP_WRITE, 0);
 	pkt->bio->bi_iter.bi_sector = new_sector;
 	pkt->bio->bi_iter.bi_size = pkt->frames * CD_FRAMESIZE;
 	pkt->bio->bi_vcnt = pkt->frames;