PCI: xgene: Drop owner assignment from platform_driver

platform_driver_register() automatically supplies THIS_MODULE, so we don't
need to set it in the platform_driver struct.

Remove the xgene_msi_driver.owner assignment.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>