iwlwifi: change the order of freeing memory

Need to free the dynamic allocated memory before ieee80211_free_hw();
once call ieee80211_free_hw(), should not reference to "priv" data
structure.

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>