Fix two small bugs with HT frequency setting:
* HT is accepted even when the driver is incapable
* HT40 is accepted when the driver cannot do 40 MHz
(both on the selected band)
Also simplify the code a little.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>