ACPI / sleep: mark acpi_sleep_dmi_check() __init

This makes a difference if the compiler decides not to inline the
function, as then the function's reference to acpisleep_dmi_table[]
yields a section mismatch warning.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>