ACPI: drop redundant owner from acpi_driver

Once all .owner is removed from all acpi_driver instances, drop it from
the structure.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>