ath9k: Update mac_postamble for AR9003 family

Enable the ALWAYS_KEYSEARCH bit in the initvals. Currently
this is done in the driver, but adding this to the initvals
makes it easier to be in sync with the INI files given
by the systems engineering team.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>