misc/mos6522: Use timer_free() in the finalize function to avoid memleak

misc/mos6522: Use timer_free() in the finalize function to avoid memleak

When running device-introspect-test, a memory leak occurred in the mos6522_init
function, this patch use timer_free() in the finalize function to fix it.

ASAN shows memory leak stack:

Direct leak of 96 byte(s) in 2 object(s) allocated from:
    #0 0xfffd5fe9e1f0 in __interceptor_calloc (/lib64/libasan.so.5+0xee1f0)
    #1 0xfffd5f7b6800 in g_malloc0 (/lib64/libglib-2.0.so.0+0x56800)
    #2 0xaaae50303d0c in timer_new_full qemu/include/qemu/timer.h:523
    #3 0xaaae50303d0c in timer_new qemu/include/qemu/timer.h:544
    #4 0xaaae50303d0c in timer_new_ns qemu/include/qemu/timer.h:562
    #5 0xaaae50303d0c in mos6522_init qemu/hw/misc/mos6522.c:490
    #6 0xaaae50b77d70 in object_init_with_type qemu/qom/object.c:371
    #7 0xaaae50b7ae84 in object_initialize_with_type qemu/qom/object.c:515
    #8 0xaaae50b7b0f8 in object_new_with_type qemu/qom/object.c:729
    #9 0xaaae50bb6d58 in qmp_device_list_properties qemu/qom/qom-qmp-cmds.c:153
    #10 0xaaae50d7e1dc in qmp_marshal_device_list_properties qemu/qapi/qapi-commands-qdev.c:59
    #11 0xaaae50dc87a0 in do_qmp_dispatch_bh qemu/qapi/qmp-dispatch.c:110
    #12 0xaaae50d931a0 in aio_bh_call qemu/util/async.c:136

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Gan Qixin <ganqixin@huawei.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20210112112705.380534-3-ganqixin@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>