ath9k: Disable ASPM only for AR9285

ath9k: Disable ASPM only for AR9285

commit 046b6802c8d3c8a57448485513bf7291633e0fa3 upstream.

Currently, ASPM is disabled for all WLAN+BT combo chipsets
when BTCOEX is enabled. This is incorrect since the workaround
is required only for WB195, which is a AR9285+AR3011 combo
solution. Fix this by checking for the HW version when enabling
the workaround.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Tested-by: Paul Stewart <pstew@chromium.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
[bwh: Backported to 3.2: ath9k_hw_get_btcoex_scheme() function is missing]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>