iwl3945: use iwl_mac_hw_scan callback

3945 can use iwl_mac_hw_scan callback instead of
iwl3945_mac_hw_scan callback.

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