iwlwifi: move iwl4965_set_pwr_src to iwl4965-base.c

This patch moves iwl4965_set_pwr_src to iwl4965-base.c.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>