block, fs, mm, drivers: use bio set/get op accessors

This patch converts the simple bi_rw use cases in the block,
drivers, mm and fs code to set/get the bio operation using
bio_set_op_attrs/bio_op

These should be simple one or two liner cases, so I just did them
in one patch. The next patches handle the more complicated
cases in a module per patch.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 3af4a5a..9fd1f63 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -485,7 +485,7 @@
 
 	bio = bio_alloc(gfp_mask, 0);
 	bio->bi_bdev = bdev;
-	bio->bi_rw = WRITE_FLUSH;
+	bio_set_op_attrs(bio, REQ_OP_WRITE, WRITE_FLUSH);
 
 	ret = submit_bio_wait(bio);