ath10k: fix 5ghz channel definitions

Nonsense channel flags were being set.

Although it doesn't seem this was visible to the
user the patch makes sure that channel
availability won't be crippled in the future if
ath_common behaviour changes.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>