ath9k: Print the correct channel mode

channelFlags doesn't contain the operating HT mode.
Use IS_CHAN_HT40 to determine if the current channel is
in HT40 mode.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>