ACPI / scan: Fix check of device_attach() return value.

Since device_attach() returns 1 on success (a driver has been bound
to the device), the check against its return value in
acpi_bus_device_attach() should modified to take that into accout.
Make it so.

[rjw: Subject and changelog.]
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>