bhyve: fix typo in struct field accessor

This fixes a FreeBSD build error from

  commit a11a0e6e
  Author: Rafael Fonseca <r4f4rfs@gmail.com>
  Date:   Tue Mar 24 17:14:30 2020 +0100

    bhyve: move video default logic to driver
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

src/bhyve/bhyve_domain.c

@@ -162,8 +162,8 @@ bhyveDomainDeviceDefPostParse(virDomainDeviceDefPtr dev,
     }
 
     if (dev->type == VIR_DOMAIN_DEVICE_VIDEO &&
-        dev->data.video.type == VIR_DOMAIN_VIDEO_TYPE_DEFAULT) {
-        dev->data.video.type = VIR_DOMAIN_VIDEO_TYPE_GOP;
+        dev->data.video->type == VIR_DOMAIN_VIDEO_TYPE_DEFAULT) {
+        dev->data.video->type = VIR_DOMAIN_VIDEO_TYPE_GOP;
     }
 
     return 0;