IB/mlx5: Fix wrong use of kfree at bad flow in create_cq_user

The kfree was called to free cqb, while it should free *cqb.

Fixes: 1cbe6fc8

 ("IB/mlx5: Add support for CQE compressing")
Signed-off-by: Bodong Wang <bodong@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>