ath9k: Add custom parameters for CUS198

CUS198 is a card based on AR9485. There are differences
between the base reference design HB125 and CUS198.
Identify such cards based on the PCI subsystem IDs and
set HW parameters appropriately.

Addresses this bug - https://bugzilla.kernel.org/show_bug.cgi?id=49201



Cc: jkp@iki.fi
Cc: gfmichaud@gmail.com
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>