ath9k: Fix COMP_BAR filter

ATH9K_RX_FILTER_COMP_BAR is used to receive BAR
completion frames and is set if the current channel
is HT. When channel contexts are enabled, instead of using
the mac80211 helpers, check if the current channel
definition is HT.

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