staging: Remove a warning for drivers/staging/wlan-ng/cfg80211.c

Hi us,
   When i was compiling kernel, a warning happened to me.
The warning said like following.

drivers/staging/wlan-ng/cfg80211.c:709: warning: initialization from
incompatible pointer type.

See http://s1202.photobucket.com/albums/bb364/harrywei/?action=view&current=patched2.png
for more details.

So i patch like following.

Signed-off-by: Harry Wei <harryxiyou@gmail.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>