RDMA/mlx5: Cancel pkey work before destroying device resources

In the driver release flow, we are ensuring that notifier is disabled and
no new works can be added to pkey_change_handler. It means that we can
cancel that handler before destroying resources to make sure that our
unwind routine is symmetrical to the allocation one.

Link: https://lore.kernel.org/r/f2b1ea1bad952e4e7a48a6f731de9e0344986b29.1627040189.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>