pci: Use bool return type for some virPCIDeviceGet*() functions

pci: Use bool return type for some virPCIDeviceGet*() functions

The affected functions are:

  virPCIDeviceGetManaged()
  virPCIDeviceGetUnbindFromStub()
  virPCIDeviceGetRemoveSlot()
  virPCIDeviceGetReprobe()

Change their return type from unsigned int to bool: the corresponding
members in struct _virPCIDevice are defined as bool, and even the
corresponding virPCIDeviceSet*() functions take a bool value as input
so there's no point in these functions having unsigned int as return
type.

Suggested-by: John Ferlan <jferlan@redhat.com>