mac80211: Fix warnings due to -Wunused-but-set-variable

mac80211: Fix warnings due to -Wunused-but-set-variable

These warnings are exposed by gcc 4.6.
net/mac80211/sta_info.c: In function 'sta_info_cleanup_expire_buffered':
net/mac80211/sta_info.c:590:32: warning: variable 'sdata' set but not used
net/mac80211/ibss.c: In function 'ieee80211_rx_mgmt_auth_ibss':
net/mac80211/ibss.c:43:34: warning: variable 'status_code' set but not used
net/mac80211/work.c: In function 'ieee80211_send_assoc':
net/mac80211/work.c:203:9: warning: variable 'len' set but not used
net/mac80211/tx.c: In function '__ieee80211_parse_tx_radiotap':
net/mac80211/tx.c:1039:35: warning: variable 'sband' set but not used
net/mac80211/mesh.c: In function 'ieee80211_mesh_rx_queued_mgmt':
net/mac80211/mesh.c:616:28: warning: variable 'ifmsh' set but not used
 ...

Signed-off-by: Rajkumar Manoharan <rmanoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>