IB/mlx5: Unify CQ create flags check

The create_cq() can receive creation flags which were used
differently by two commits which added create_cq extended
command and cross-channel. The merged code caused to not
accept any flags at all.

This patch unifies the check into one function and one return
error code.

Fixes: 972ecb82 ("IB/mlx5: Add create_cq extended command")
Fixes: 051f2630 ("IB/mlx5: Add driver cross-channel support")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>