net/mlx5: Fix mlx5_core_destroy_cq() error flow

The firmware command to destroy a CQ might fail when the object is
referenced by other object and the ref count is managed by the firmware.

To enable a second successful destruction post the first failure need to
change  mlx5_eq_del_cq() to be a void function.

As an error in mlx5_eq_del_cq() is quite fatal from the option to
recover, a debug message inside it should be good enougth and it was
changed to be void.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>