The single doorbell completion scan took a cleared doorbell bit as a
completion. A bit that was never set reads the same, so a slot whose
doorbell was not rung yet, or one that a reset wiped, looked complete
and was finished with a stale descriptor.

UFSHCI 3.0 added UTRLCNR, which the controller sets when it completes
a request and the driver already clears afterwards. Use it to find
completed slots on a 3.0 or later controller. Older controllers keep
the doorbell check, and the task management list has no such register.

Sponsored by: Samsung Electronics