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/block/umem.c b/drivers/block/umem.c
index 7939b9f..4b3ba74 100644
--- a/drivers/block/umem.c
+++ b/drivers/block/umem.c
@@ -462,7 +462,7 @@
 				le32_to_cpu(desc->local_addr)>>9,
 				le32_to_cpu(desc->transfer_size));
 			dump_dmastat(card, control);
-		} else if ((bio->bi_rw & REQ_WRITE) &&
+		} else if (op_is_write(bio_op(bio)) &&
 			   le32_to_cpu(desc->local_addr) >> 9 ==
 				card->init_size) {
 			card->init_size += le32_to_cpu(desc->transfer_size) >> 9;