block, drivers, cgroup: use op_is_write helper instead of checking for REQ_WRITE

We currently set REQ_WRITE/WRITE for all non READ IOs
like discard, flush, writesame, etc. In the next patches where we
no longer set up the op as a bitmap, we will not be able to
detect a operation direction like writesame by testing if REQ_WRITE is
set.

This patch converts the drivers and cgroup to use the
op_is_write helper. This should just cover the simple
cases. I did dm, md and bcache in their own patches
because they were more involved.

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/drivers/scsi/osd/osd_initiator.c b/drivers/scsi/osd/osd_initiator.c
index 3b11aad..14ed39b 100644
--- a/drivers/scsi/osd/osd_initiator.c
+++ b/drivers/scsi/osd/osd_initiator.c
@@ -824,7 +824,7 @@
 {
 	_osd_req_encode_common(or, OSD_ACT_WRITE, obj, offset, len);
 	WARN_ON(or->out.bio || or->out.total_bytes);
-	WARN_ON(0 == (bio->bi_rw & REQ_WRITE));
+	WARN_ON(!op_is_write(bio_op(bio)));
 	or->out.bio = bio;
 	or->out.total_bytes = len;
 }
@@ -875,7 +875,7 @@
 {
 	_osd_req_encode_common(or, OSD_ACT_READ, obj, offset, len);
 	WARN_ON(or->in.bio || or->in.total_bytes);
-	WARN_ON(bio->bi_rw & REQ_WRITE);
+	WARN_ON(op_is_write(bio_op(bio)));
 	or->in.bio = bio;
 	or->in.total_bytes = len;
 }