hw/char/exynos4210_uart: Fix memleaks in exynos4210_uart_init

hw/char/exynos4210_uart: Fix memleaks in exynos4210_uart_init

It's easy to reproduce as follow:
virsh qemu-monitor-command vm1 --pretty '{"execute": "device-list-properties",
"arguments":{"typename":"exynos4210.uart"}}'

ASAN shows memory leak stack:
  #1 0xfffd896d71cb in g_malloc0 (/lib64/libglib-2.0.so.0+0x571cb)
  #2 0xaaad270beee3 in timer_new_full /qemu/include/qemu/timer.h:530
  #3 0xaaad270beee3 in timer_new /qemu/include/qemu/timer.h:551
  #4 0xaaad270beee3 in timer_new_ns /qemu/include/qemu/timer.h:569
  #5 0xaaad270beee3 in exynos4210_uart_init /qemu/hw/char/exynos4210_uart.c:677
  #6 0xaaad275c8f4f in object_initialize_with_type /qemu/qom/object.c:516
  #7 0xaaad275c91bb in object_new_with_type /qemu/qom/object.c:684
  #8 0xaaad2755df2f in qmp_device_list_properties /qemu/qom/qom-qmp-cmds.c:152

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200213025603.149432-1-kuhn.chenqun@huawei.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>