x86/cpuid: Plug memory leak in cpudef_setfield()

To reproduce the leak, put two name options into the same [cpudef]
section of target-x86_64.conf.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

target-i386/cpuid.c

@@ -950,6 +950,7 @@ static int cpudef_setfield(const char *name, const char *str, void *opaque)
     int err = 0;
 
     if (!strcmp(name, "name")) {
+        g_free((void *)def->name);
         def->name = g_strdup(str);
     } else if (!strcmp(name, "model_id")) {
         strncpy(def->model_id, str, sizeof (def->model_id));