ath9k: Fix PHY restart workaround

The PHY restart workaround that handles baseband hangs
for packets with unsupported rates is required only
for a HW bug in AR9300 v2.2. All the subsequent chips in
the AR9003 family do not require this driver fix since
it has been addressed in the HW.

Since the value of the AR_PHY_RESTART register is written
with the default initvals, make sure that PHY restart is
always disabled once this particular BB hang signaure has
been encountered.

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