wireless:hostap_ap.c Fix warning: variable 'fc' set but not used

The below patch fixes a warning message when compiling with gcc 4.6.0
  CC [M]  drivers/net/wireless/hostap/hostap_ap.o
drivers/net/wireless/hostap/hostap_ap.c: In function 'hostap_ap_tx_cb_assoc':
drivers/net/wireless/hostap/hostap_ap.c:691:6: warning: variable 'fc' set but not used

Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>

Signed-off-by: John W. Linville <linville@tuxdriver.com>