staging:wlan-ng: clean p80211req_handlemsg

the switch case doesn't have a break statement of DIDmsg_dot11req_mibget,
and DIDmsg_dot11req_mibset cases, and also cleanup the code to follow
the kernel coding way

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