iwl3945: Have consistant and not redefined HW constants

SRAM addresses are different for 3945, 4065, and 5000, let's give them
different names.
Also, the RSSI_OFFSET is different for 3945 and 4965, thus they should be
named differently.

Signed-off-by: Samuel Ortiz <samuel.ortiz@intel.com>
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>