Avoid using magic values for CCK frequency bits. Also the mask we were
using for the requested frequency was one bit too short. Fix it up.

Note: This also fixes the #define for a mask (spotted by Jesse in his
review).
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
[danvet: Add note about mask change.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>