kern/58086: genfb_attach returns useless int

[campbell+netbsd%mumble.net@localhost]

>Number:         58086
>Category:       kern
>Synopsis:       genfb_attach returns useless int
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Mar 28 19:00:00 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current
>Organization:
The NetFBSD Foundatoin
>Environment:
>Description:
The genfb_attach function never fails, and no callers are prepared to handle failure, but it returns 0 as int.
>How-To-Repeat:
code inspection
>Fix:
Change it to return void instead.