hp-wmi: remove a variable that is never read

Remove the status variable from hp_wmi_perform_query which holds the
return value from wmi_evaluate_method(). It is never checked as the
function bails out if the output buffer hasn't been allocated which
indicates the call failed.

Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Matthew Garrett <mjg@redhat.com>