iwl3945: Getting rid of priv->antenna

The iwl_priv antenna field is useless as we can simply use the corresponding
mod_params antenna field.

Signed-off-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>