ath9k_hw: Relocate Opmode initialization

Programming the opmode in the HW can be done
before the assoc_id and STA_ID registers are
setup. This helps ath9k_htc when multiple register
writes are used.

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