PCI/IOV: Simplify pci-pf-stub with module_pci_driver()

Use the module_pci_driver() macro to make the code simpler by eliminating
module_init() and module_exit() calls.

Link: https://lore.kernel.org/r/20200917071042.1909191-1-liushixin2@huawei.com


Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>