ath9k: Cleanup __ath9k_hw_init()

* Move initialization of config variables to
  ath9k_hw_init_config().

* Move initialization of defaults to ath9k_hw_init_defaults().

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