ath9k_htc: Fix disconnect issue in HT40 mode.

ath9k_htc: Fix disconnect issue in HT40 mode.

commit 71ba186c123630ddab17667ec9ecf7e2ef211295 upstream.

Some APs advertise that they may be HT40 capable in the capabilites
but the current operating channel configuration may be only HT20.
This causes disconnection as ath9k_htc sets WLAN_RC_40_FLAG despite
the AP operating in HT20 mode.
Hence set this flag only if the current channel configuration
is HT40 enabled.

Signed-off-by: Vivek Natarajan <vnatarajan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>