When running device-introspect-test, a memory leak occurred in the a10_pit_init
function, so use ptimer_free() in the finalize function to avoid it.

ASAN shows memory leak stack:

Indirect leak of 288 byte(s) in 6 object(s) allocated from:
    #0 0xffffab97e1f0 in __interceptor_calloc (/lib64/libasan.so.5+0xee1f0)
    #1 0xffffab256800 in g_malloc0 (/lib64/libglib-2.0.so.0+0x56800)
    #2 0xaaabf555db84 in timer_new_full /qemu/include/qemu/timer.h:523
    #3 0xaaabf555db84 in timer_new /qemu/include/qemu/timer.h:544
    #4 0xaaabf555db84 in timer_new_ns /qemu/include/qemu/timer.h:562
    #5 0xaaabf555db84 in ptimer_init /qemu/hw/core/ptimer.c:433
    #6 0xaaabf57415e8 in a10_pit_init /qemu/hw/timer/allwinner-a10-pit.c:278
    #7 0xaaabf6339f6c in object_initialize_with_type /qemu/qom/object.c:515
    #8 0xaaabf633ca04 in object_initialize_child_with_propsv /qemu/qom/object.c:564
    #9 0xaaabf633cc08 in object_initialize_child_with_props /qemu/qom/object.c:547
    #10 0xaaabf5b94680 in aw_a10_init /qemu/hw/arm/allwinner-a10.c:49
    #11 0xaaabf6339f6c in object_initialize_with_type /qemu/qom/object.c:515
    #12 0xaaabf633a1e0 in object_new_with_type /qemu/qom/object.c:729

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Gan Qixin <ganqixin@huawei.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>