pl031: Use timer_free() in the finalize function to avoid memleaks

pl031: Use timer_free() in the finalize function to avoid memleaks

When running device-introspect-test, a memory leak occurred in the pl031_init
function, this patch use timer_free() in the finalize function to fix it.

ASAN shows memory leak stack:

Direct leak of 48 byte(s) in 1 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 0xaaabf5621cfc in timer_new_full qemu/include/qemu/timer.h:523
    #3 0xaaabf5621cfc in timer_new qemu/include/qemu/timer.h:544
    #4 0xaaabf5621cfc in timer_new_ns qemu/include/qemu/timer.h:562
    #5 0xaaabf5621cfc in pl031_init qemu/hw/rtc/pl031.c:194
    #6 0xaaabf6339f6c in object_initialize_with_type qemu/qom/object.c:515
    #7 0xaaabf633a1e0 in object_new_with_type qemu/qom/object.c:729
    #8 0xaaabf6375e40 in qmp_device_list_properties qemu/qom/qom-qmp-cmds.c:153
    #9 0xaaabf5a95540 in qdev_device_help qemu/softmmu/qdev-monitor.c:283
    #10 0xaaabf5a96940 in qmp_device_add qemu/softmmu/qdev-monitor.c:801
    #11 0xaaabf5a96e70 in hmp_device_add qemu/softmmu/qdev-monitor.c:916
    #12 0xaaabf5ac0a2c in handle_hmp_command qemu/monitor/hmp.c:1100

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Gan Qixin <ganqixin@huawei.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20210112112705.380534-2-ganqixin@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>