pci_get_bus_and_slot — locate PCI device from a given PCI bus & slot
number of PCI bus on which desired PCI device resides
encodes number of PCI slot in which the desired PCI device resides and the logical device number within that slot in case of multi-function devices.
the bus/slot search is limited to PCI domain (segment) 0.
Given a PCI bus and slot/function number, the desired PCI device is located in system global list of PCI devices. If the device is found, a pointer to its data structure is returned. If no device is found, NULL is returned. The returned device has its reference count bumped by one.