cfg80211: explicitly initialize some fields in custom reg path

Explicitly initialize the DFS state and beacon found state when handling
channels in the custom regulatory path.

Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Acked-by: Luis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>