ath9k: Enable PLL fix only for AR9340/AR9330

ath9k: Enable PLL fix only for AR9340/AR9330

The PLL hang workaround is required only for AR9330 and
AR9340. This issue was first observed on an AP121 and the WAR
is enabled for AR9340 also (DB120 etc.), since it uses a PLL
design identical to AR9330. This is not required for AR9485 and AR9550.

Various bugs have been reported regarding this:

https://bugzilla.redhat.com/show_bug.cgi?id=997217
https://bugzilla.redhat.com/show_bug.cgi?id=994648

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