iwlwifi: fix rate scale TLC column selection bug

This patch fixes a case that a wrong maximal rate is selected when
searching for better configurations.

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