iommu/vt-d: Remove unnecessary checks in iopf disabling path

iommu/vt-d: Remove unnecessary checks in iopf disabling path

iommu_unregister_device_fault_handler() and iopf_queue_remove_device()
are called after device has stopped issuing new page falut requests and
all outstanding page requests have been drained. They should never fail.
Trigger a warning if it happens unfortunately.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20230324120234.313643-7-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>