ACPI: acpi_bus_unregister_driver() returns void

Nobody looks at the return value, and this brings it into line with
pci_unregister_driver(), etc.  Also removed validation of the driver
pointer passed in to register and unregister.  More consistent, and we'll
find bugs faster if we fault rather than returning an error that's ignored.

Also makes internal functions acpi_device_unregister() and
acpi_driver_detach() void, since nobody uses their returns either.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>