iwlwifi: fix iwl_mac_set_key and iwl3945_mac_set_key

This patch fix iwl_mac_set_key function changed in patch
"mac80211: clean up set_key callback"

1. removing 'static' const u8 *addr' that can possible cause
conflict when two or more NICs are present in the system.
2. simplifying functions

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>