pds_core: Cancel AQ work on teardown

There is a small window where pdsc_work_thread()
calls pdsc_process_adminq() and pdsc_process_adminq()
passes the PDSC_S_STOPPING_DRIVER check and starts
to process adminq/notifyq work and then the driver
starts a fw_down cycle. This could cause some
undefined behavior if the notifyqcq/adminqcq are
free'd while pdsc_process_adminq() is running. Use
cancel_work_sync() on the adminqcq's work struct
to make sure any pending work items are cancelled
and any in progress work items are completed.

Also, make sure to not call cancel_work_sync() if
the work item has not be initialized. Without this,
traces will happen in cases where a reset fails and
teardown is called again or if reset fails and the
driver is removed.

Fixes: 01ba61b5

 ("pds_core: Add adminq processing and commands")
Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://lore.kernel.org/r/20240129234035.69802-3-brett.creeley@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>