tree-wide: use mfree more

src/machine/machine.c

@@ -80,9 +80,7 @@ Machine* machine_new(Manager *manager, MachineClass class, const char *name) {
 fail:
         free(m->state_file);
         free(m->name);
-        free(m);
-
-        return NULL;
+        return mfree(m);
 }
 
 void machine_free(Machine *m) {

src/machine/operation.c

@@ -147,6 +147,5 @@ Operation *operation_free(Operation *o) {
         if (o->machine)
                 LIST_REMOVE(operations_by_machine, o->machine->operations, o);
 
-        free(o);
-        return NULL;
+        return mfree(o);
 }