lm32: do not leak memory on object_new/object_unref

lm32: do not leak memory on object_new/object_unref

Bottom halves and ptimers are malloced, but nothing in these
files is freeing memory allocated by instance_init.  Since
these are sysctl devices that are never unrealized, just moving
the allocations to realize is enough to avoid the leak in
practice (and also to avoid upsetting asan when running
device-introspect-test).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>