iwlwifi: fix bug when moving from 11gn to 11a or 11an to 11g

It is wrong to set the rxon channel according to the ht-channel
in case there is a mismatch (e.g. when there is no ht).

Signed-off-by: Guy Cohen <guy.cohen@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>