RDMA/mlx5: Properly check return value of mlx5_get_uars_page

Starting from commit 72f36be06138 ("net/mlx5: Fix mlx5_get_uars_page to
return error code") the mlx5_get_uars_page() call returns error in case
of failure, but it was mistakenly overlooked in the merge commit.

Fixes: e7996a9a77fc ("Merge tag v4.15 of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git")
Reported-by: Alaa Hleihel <alaa@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/main.c

@@ -5426,9 +5426,7 @@ static void mlx5_ib_stage_cong_debugfs_cleanup(struct mlx5_ib_dev *dev)
 static int mlx5_ib_stage_uar_init(struct mlx5_ib_dev *dev)
 {
 	dev->mdev->priv.uar = mlx5_get_uars_page(dev->mdev);
-	if (!dev->mdev->priv.uar)
-		return -ENOMEM;
-	return 0;
+	return PTR_ERR_OR_ZERO(dev->mdev->priv.uar);
 }
 
 static void mlx5_ib_stage_uar_cleanup(struct mlx5_ib_dev *dev)