By code inspection, the freeze_work is never canceled.

Fix by adding a cancel_work_sync in the shutdown path to insure it is no
longer running.

Fixes: 77241056 ("IB/hfi1: add driver files")
Reviewed-by: NMichael J. Ruhl <michael.j.ruhl@intel.com>
Reviewed-by: NDennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: NMike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: NDennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>