iwlwifi: name changed from "fat" to "ht40"

Rename "fat" to "ht40"
The term "fat channel" is deprecated in favor of "HT40"

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>