mac80211: properly set CCK flag in radiotap

Fix a regression introduced by commit a5e70697 ("mac80211: add radiotap flag
and handling for 5/10 MHz") where the IEEE80211_CHAN_CCK channel type flag was
incorrectly replaced by the IEEE80211_CHAN_OFDM flag. This commit fixes that by
using the CCK flag again.

Cc: stable@vger.kernel.org
Fixes: a5e70697 ("mac80211: add radiotap flag and handling for 5/10 MHz")
Signed-off-by: Mathy Vanhoef <vanhoefm@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>