vfio-pci: Add dummy PCI ROM write accessor

Just to be sure we don't jump off any NULL pointer cliffs.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
vfio-pci: Fix endian issues in vfio_pci_size_rom()

VFIO is always little endian so do byte swapping of our mask on the
way in and byte swapping of the size on the way out.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>