Input: soc_button_array - fix leaking the ACPI button descriptor buffer

We are passing a buffer with ACPI_ALLOCATE_BUFFER set to
acpi_evaluate_object, so we must free it when we are done with it.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>