coresight: Fix memory leak in acpi_buffer->pointer

There are memory leaks reported by kmemleak:
...
unreferenced object 0xffff00213c141000 (size 1024):
  comm "systemd-udevd", pid 2123, jiffies 4294909467 (age 6062.160s)
  hex dump (first 32 bytes):
    04 00 00 00 02 00 00 00 18 10 14 3c 21 00 ff ff  ...........<!...
    00 00 00 00 00 00 00 00 03 00 00 00 10 00 00 00  ................
  backtrace:
    [<000000004b7c9001>] __kmem_cache_alloc_node+0x2f8/0x348
    [<00000000b0fc7ceb>] __kmalloc+0x58/0x108
    [<0000000064ff4695>] acpi_os_allocate+0x2c/0x68
    [<000000007d57d116>] acpi_ut_initialize_buffer+0x54/0xe0
    [<0000000024583908>] acpi_evaluate_object+0x388/0x438
    [<0000000017b2e72b>] acpi_evaluate_object_typed+0xe8/0x240
    [<000000005df0eac2>] coresight_get_platform_data+0x1b4/0x988 [coresight]
...

The ACPI buffer memory (buf.pointer) should be freed. But the buffer
is also used after returning from acpi_get_dsd_graph().
Move the temporary variables buf to acpi_coresight_parse_graph(),
and free it before the function return to prevent memory leak.

Fixes: 76ffa5ab

 ("coresight: Support for ACPI bindings")
Signed-off-by: Junhao He <hejunhao3@huawei.com>
Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230817085937.55590-2-hejunhao3@huawei.com