acpi_install_notify_handler() could fail.  So check the exit status
and give a better debug info.
Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>