iwlwifi/iwl3945 : unify apm stop operation

Unify the usage of apm_stop_master and apm_stop
across all hardwares.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>