net/mlx5_core,mlx5_ib: Do not use vmap() on coherent memory

As David Daney pointed in mlx4_core driver [1], mlx5_core is also
misusing the DMA-API.

This patch is removing the code that vmap() memory allocated by
dma_alloc_coherent().

After this patch, users of this drivers might fail allocating resources
on memory fragmeneted systems.  This will be fixed later on.

[1] - https://patchwork.ozlabs.org/patch/458531/

CC: David Daney <david.daney@cavium.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/infiniband/hw/mlx5/qp.c b/drivers/infiniband/hw/mlx5/qp.c
index d35f62d..426eb88 100644
--- a/drivers/infiniband/hw/mlx5/qp.c
+++ b/drivers/infiniband/hw/mlx5/qp.c
@@ -768,7 +768,7 @@
 	qp->sq.offset = qp->rq.wqe_cnt << qp->rq.wqe_shift;
 	qp->buf_size = err + (qp->rq.wqe_cnt << qp->rq.wqe_shift);
 
-	err = mlx5_buf_alloc(dev->mdev, qp->buf_size, PAGE_SIZE * 2, &qp->buf);
+	err = mlx5_buf_alloc(dev->mdev, qp->buf_size, &qp->buf);
 	if (err) {
 		mlx5_ib_dbg(dev, "err %d\n", err);
 		goto err_uuar;