iwlwifi: remove pointless HT check

Remove the check before invoking iwl_set_ht_add_station(),
since neither of the conditions in this check makes sense,
as either we pass in a NULL ht_info (first branch) or in
the IBSS case an ht_info with ht_enabled=false.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>