staging:wlan-ng: p80211req_mibset_mibget should be void

this function always returning 0, there are no callers that checks
the return of this function, make this function return void

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>