bnxt_en: Fix regression in workqueue cleanup logic in bnxt_remove_one().

A recent patch has moved the workqueue cleanup logic before
calling unregister_netdev() in bnxt_remove_one().  This caused a
regression because the workqueue can be restarted if the device is
still open.  Workqueue cleanup must be done after unregister_netdev().
The workqueue will not restart itself after the device is closed.

Call bnxt_cancel_sp_work() after unregister_netdev() and
call bnxt_dl_fw_reporters_destroy() after that.  This fixes the
regession and the original NULL ptr dereference issue.

Fixes: b16939b5

 ("bnxt_en: Fix NULL ptr dereference crash in bnxt_fw_reset_task()")
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>