mac80211: DFS setup chandef for radar_event correctly

Setup chandef for radar event correctly, before we
will clear this in ieee80211_dfs_cac_cancel() function.

Without this patch mac80211 will report wrong channel
width in case we will get radar event during active CAC.

Signed-off-by: Janusz Dziedzic <janusz.dziedzic@tieto.com>
Reviewed-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>