PCI: Short-circuit pci_device_is_present() for disconnected devices

If the PCI device is disconnected, return false immediately from
pci_device_is_present().  pci_device_is_present() uses the bus accessors,
so the early return in the device accessors doesn't help here.

Tested-by: Krishna Dhulipala <krishnad@fb.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Wei Zhang <wzhang@fb.com>