spapr_pci: Fix obsolete comment about MSIX encoding in addr/data

f1c2dc7c866a "spapr-pci: rework MSI/MSIX" (07/2013) changed MSIX encoding
but forgot to change the comment so this changes it.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
1 file changed