Fix tests to include video ram size

My commit 3e42867 started filling out the video size in post-parse,
but did not adjust the tests.

tests/xmconfigdata/test-pci-devs.xml

@@ -49,7 +49,7 @@
     <input type='keyboard' bus='ps2'/>
     <graphics type='vnc' port='-1' autoport='yes'/>
     <video>
-      <model type='cirrus' heads='1' primary='yes'/>
+      <model type='cirrus' vram='16384' heads='1' primary='yes'/>
     </video>
     <hostdev mode='subsystem' type='pci' managed='no'>
       <source>