platform/x86: mxm-wmi: fix memleak in mxm_wmi_call_mx[ds|mx]()

platform/x86: mxm-wmi: fix memleak in mxm_wmi_call_mx[ds|mx]()

The ACPI buffer memory (out.pointer) returned by wmi_evaluate_method()
is not freed after the call, so it leads to memory leak.

The method results in ACPI buffer is not used, so just pass NULL to
wmi_evaluate_method() which fixes the memory leak.

Fixes: 99b38b4acc0d ("platform/x86: add MXM WMI driver.")
Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Link: https://lore.kernel.org/r/20221129011101.2042315-1-liaoyu15@huawei.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>