Use completion to wait on ITCT CLR interrupt finishing before
processing other things when freeing a device.

This is safer than the pre-existing process of polling the register.
Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>