libxl: add missing 'break' from commit 1298daca

Add missing 'break's from commit 1298daca, as noted by John Ferlan

https://www.redhat.com/archives/libvir-list/2014-October/msg00430.html

src/libxl/libxl_domain.c

@@ -522,6 +522,7 @@ libxlDomainDeviceDefPostParse(virDomainDeviceDefPtr dev,
                 else
                     dev->data.video->vram = 8 * 1024;
                 }
+            break;
         case VIR_DOMAIN_VIDEO_TYPE_CIRRUS:
             if (dev->data.video->vram == 0) {
                 if (dm_type == LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN)
@@ -529,6 +530,7 @@ libxlDomainDeviceDefPostParse(virDomainDeviceDefPtr dev,
                 else
                     dev->data.video->vram = 4 * 1024;
             }
+            break;
         }
     }