ACPI / TPM: fix memory leak when walking ACPI namespace

In function ppi_callback(), memory allocated by acpi_get_name() will get
leaked when current device isn't the desired TPM device, so fix the
memory leak.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>