ath9k_hw: simplify revision checks for AR9285

Since AR9285 v1.0 and v1.1 were never sold (and the initvals removed),
its revision checks can be simplified similar to AR9280

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>