ath9k: Use correct channel for RX packets

Accessing the current channel definition in mac80211
when processing RX packets is problematic because it
could have been updated when a scan is issued. Since a
channel change involves flushing the existing packets
in the RX queue before a chip-reset is done, they would
be processed using the wrong band/channel information.

To avoid this, use the current channel information
maintained in the driver.

Cc: stable@vger.kernel.org
Reported-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>