ACPI: asus_acpi: Do not load if no device has been found

asus_acpi_init() has a hack to prevent the driver from loading
when asus_hotk_add() fails.  However, it was returning the successful
return value of acpi_bug_registger_driver() on failure.  This caused
an oops on unload.  Instead it should return -ENODEV.

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>