RDMA/core: Stop DIM before destroying CQ

HW destroy operation should be last operation after all possible CQ users
completed their work, so move DIM work cancellation before such destroy
call.

Fixes: da662979

 ("RDMA/core: Provide RDMA DIM support for ULPs")
Link: https://lore.kernel.org/r/20200730082719.1582397-3-leon@kernel.org
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>