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>

drivers/md/dm-mpath.c

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index d7107d2..ac734e5 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -661,7 +661,7 @@
 
 	bio->bi_error = 0;
 	bio->bi_bdev = pgpath->path.dev->bdev;
-	bio->bi_rw |= REQ_FAILFAST_TRANSPORT;
+	bio->bi_opf |= REQ_FAILFAST_TRANSPORT;
 
 	if (pgpath->pg->ps.type->start_io)
 		pgpath->pg->ps.type->start_io(&pgpath->pg->ps,