wireless: fix kernel-doc warning in net/cfg80211.h

Fix kernel-doc warning in net/cfg80211.h:

Warning(include/net/cfg80211.h:1884): No description found for parameter 'registered'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>