ath9k: Handle ASPM properly

ASPM has to be disabled when BTCOEX is in use, do this properly
by calling the bus-specific ASPM init routine after the
BTCOEX scheme has been determined.

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