iwlwifi-5000: use iwl4965_set_pwr_src in 5000

This patch makes use of iwl4965_set_pwr_src in 5000 HW family

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