acpi: Fix setting sleep state sysctls to NONE

This restores the functionality as it was pre-97d152698f48.

A stopgap was committed by glebius@ in 34dfccc64f47 ("acpi: in
acpi_stype_sysctl() use same logic as in acpi_sleep_state_sysctl()").

PR: 290651
Reviewed by: thj, emaste
Approved by: thj
Fixes: 97d152698f48 ("acpi: Use sleep types defined in sys/power.h")
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D53909