ACPI: SBS: Simplify the driver init code

acpi_bus_register_driver() will check acpi_disable and return
-ENODEV, so the acpi_disable check outside the
acpi_bus_register_driver() is duplicated, can be removed.

Also we can just return from acpi_bus_register_driver() then
we can simplify the code further.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>