acpi: in acpi_stype_sysctl() use same logic as in acpi_sleep_state_sysctl()
Otherwise we allow to trigger an MPASS() by a userland sysctl, e.g.
hw.acpi.power_button_state=NONE. This does not bring fully compatibility,
where as before 97d152698f483 setting to 'NONE' actually meant disabling
any action on a power or sleep button. Now sysctl will fail, but with
this change it won't at least panic.
Aymeric may come with a better fix.