nvmet: add unlikely check at nvmet_req_alloc_sgl

The call to sgl_alloc shouldn't fail so add this simple optimization to
the fast path.
Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/target/core.c

@@ -966,7 +966,7 @@ int nvmet_req_alloc_sgl(struct nvmet_req *req)
 	}
 
 	req->sg = sgl_alloc(req->transfer_len, GFP_KERNEL, &req->sg_cnt);
-	if (!req->sg)
+	if (unlikely(!req->sg))
 		return -ENOMEM;
 
 	return 0;