AMD/IOMMU: replace a few PCI_BDF2()

AMD/IOMMU: replace a few PCI_BDF2()

struct pci_dev has the wanted value directly available; use it. Note
that this fixes a - imo benign - mistake in reassign_device(): The unity
map removal ought to be based on the passed in devfn (as is the case on
the establishing side). This is benign because the mappings would be
removed anyway a little later, when the "main" device gets processed.
While there also limit the scope of two variables in that function.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>