kern/57575: pmf_device_register should return void

[campbell+netbsd%mumble.net@localhost]

>Number:         57575
>Category:       kern
>Synopsis:       pmf_device_register should return void
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Aug 09 07:30:00 +0000 2023
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetBSD FoundationWARNING: couldn't establish power handler
>Environment:
>Description:
pmf_device_register never fails.  Failure here is not useful.  Every branch on the return value is dead code.
>How-To-Repeat:
code inspection
>Fix:
1. Change pmf_device_register to return void.
2. Prune a zillion dead branches, maybe with the help of coccinelle.