tests: fix xml2xml tpm-emulator.xml test

It is failing, because it ends up being parsed with version='default'
and expects '1.2' instead.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

tests/qemuxml2argvdata/tpm-emulator.xml

@@ -23,7 +23,7 @@
     <input type='mouse' bus='ps2'/>
     <input type='keyboard' bus='ps2'/>
     <tpm model='tpm-tis'>
-      <backend type='emulator'/>
+      <backend type='emulator' version='1.2'/>
     </tpm>
     <memballoon model='virtio'/>
   </devices>