PM: Prevent waiting forever on asynchronous resume after failing suspend

During suspend, the power.completion is expected to be set when a
device has not yet started suspending. Set it on init to fix a
corner case where a device is resumed when its parent has never
suspended.

Consider three drivers, A, B, and C. The parent of A is C, and C
has async_suspend set. On boot, C->power.completion is initialized
to 0.

During the first suspend:
suspend_devices_and_enter(...)
dpm_resume(...)
device_suspend(A)
device_suspend(B) returns error, aborts suspend
dpm_resume_end(...)
dpm_resume(...)
device_resume(A)
dpm_wait(A->parent == C)
wait_for_completion(C->power.completion)

The wait_for_completion will never complete, because
complete_all(C->power.completion) will only be called from
device_suspend(C) or device_resume(C), neither of which is called
if suspend is aborted before C.

After a successful suspend->resume cycle, where B doesn't abort
suspend, C->power.completion is left in the completed state by the
call to device_resume(C), and the same call path will work if B
aborts suspend.

Signed-off-by: Colin Cross <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/base/power/main.c

···
 {
 	dev->power.status = DPM_ON;
 	init_completion(&dev->power.completion);
+	complete_all(&dev->power.completion);
 	dev->power.wakeup_count = 0;
 	pm_runtime_init(dev);
 }