net/mlx5: Set completion EQs as shared resources

Mark completion EQs as shared resources so that they can be used by CQs
with uid != 0.

Fixes: 7efce369 ("IB/mlx5: Add obj create and destroy functionality")
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>