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/include/linux/bio.h b/include/linux/bio.h
index e09a889..59ffaa6 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -95,7 +95,7 @@
 
 static inline bool bio_mergeable(struct bio *bio)
 {
-	if (bio->bi_rw & REQ_NOMERGE_FLAGS)
+	if (bio->bi_opf & REQ_NOMERGE_FLAGS)
 		return false;
 
 	return true;
@@ -318,7 +318,7 @@
 
 static inline struct bio_integrity_payload *bio_integrity(struct bio *bio)
 {
-	if (bio->bi_rw & REQ_INTEGRITY)
+	if (bio->bi_opf & REQ_INTEGRITY)
 		return bio->bi_integrity;
 
 	return NULL;