vl.c: Fix memory leak in qemu_register_machine()

Since commit 261747f1 (vl: Use MachineClass instead of global
QEMUMachine list) valgrind complains about the following:

==54082== 57 bytes in 3 blocks are definitely lost in loss record 365 of
729
==54082==    at 0x4031AFE: malloc (vg_replace_malloc.c:292)
==54082==    by 0x4145569: g_malloc (in
/usr/lib64/libglib-2.0.so.0.3400.2)
==54082==    by 0x415F9E9: g_strconcat (in
/usr/lib64/libglib-2.0.so.0.3400.2)
==54082==    by 0x80157FE7: qemu_register_machine (vl.c:1597)
==54082==    by 0x80208E6B: module_call_init (module.c:105)
==54082==    by 0x80013B91: main (vl.c:3000)

Turns out that valgrind is right. We simply forget the memory that
g_strconcat() has allocated. Lets free it after the type_register().
We need a 2nd variable due to constness of the name part of the
type structure.
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NAndreas Färber <afaerber@suse.de>

vl.c

@@ -1587,14 +1587,16 @@ static void machine_class_init(ObjectClass *oc, void *data)
 
 int qemu_register_machine(QEMUMachine *m)
 {
+    char *name = g_strconcat(m->name, TYPE_MACHINE_SUFFIX, NULL);
     TypeInfo ti = {
-        .name       = g_strconcat(m->name, TYPE_MACHINE_SUFFIX, NULL),
+        .name       = name,
         .parent     = TYPE_MACHINE,
         .class_init = machine_class_init,
         .class_data = (void *)m,
     };
 
     type_register(&ti);
+    g_free(name);
 
     return 0;
 }