xen: fix condition for skipping virtio-mmio defines

GUEST_VIRTIO_MMIO_* was added in Xen 4.17, so only define them
for CONFIG_XEN_CTRL_INTERFACE_VERSIONs up to 4.16.

Reported-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed