conf: Don't leak 'ram' video property on error

It's only freed on normal returns from virDomainVideoDefParseXML,
but not when erroring out.

src/conf/domain_conf.c

@@ -7736,6 +7736,7 @@ virDomainVideoDefParseXML(const xmlNodePtr node,
 error:
     virDomainVideoDefFree(def);
     VIR_FREE(type);
+    VIR_FREE(ram);
     VIR_FREE(vram);
     VIR_FREE(heads);
     return NULL;