ath9k: Fix bug in ANI channel handling

When processing MIB interrupts, OFDM and CCK error
handling routines for low RSSI values have to be invoked
only when the channel mode is 11G/11B. Since HT channels
will also fall under the bands 2Ghz/5Ghz, check appropriately.

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