ath9k: use chandef instead of channel_type

To enable support for 5/10 MHz, some internal functions must be
converted from using the (old) channel_type to chandef. This is a good
chance to change all remaining occurences.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>