iwlwifi: eliminate power_data_39.

This patch eliminates 3945 power_data structure and make use of
of iwl_power_data.

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