ACPI: change acpi_sleep_proc_init() to return void

This patch changes the type of the return value of the acpi_sleep_proc_init()
method to be void, as this method never fails and its return value is never
used.

Signed-off-by: Rami Rosen <ramirose@gmail.com&gt;\>
[ rjw : Fixed up the static inline stub ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>