net: libwx: fix VF illegal register access

In the Linux kernel, the following vulnerability has been resolved: net: libwx: fix VF illegal register access Register WX_CFG_PORT_ST is a PF restricted register. When a VF is initialized, attempting to read this register triggers an illegal register access, which lead to a system hang. When the device is VF, the bus function ID can be obtained directly from the PCI_FUNC(pdev->devfn).