cfg80211: drop duplicated documentation of field "registered"

Field "registered" was documented three times: twice in the
documentation block of struct wiphy and once inside the struct
definition. This patch keep only one comment.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200221115604.594035-3-Jerome.Pouiller@silabs.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>