staging: rtl8188eu: issue_probersp(): remove unused parameter

The is_valid_p2p_probereq is never referenced in the function body.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>