nvme: add NVME_SC_CANCELLED

To properly document how we are using a negative Linux error value to
communicate request cancellations inside the driver.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 99c5b63..e683bd1 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -621,7 +621,7 @@
 
 		if (req->cmd_type == REQ_TYPE_DRV_PRIV) {
 			if (cmd_rq->ctx == CMD_CTX_CANCELLED)
-				error = -EINTR;
+				error = NVME_SC_CANCELLED;
 			else
 				error = status;
 		} else {