ath9k: fix regression which disabled ps on ath9k

ath9k: fix regression which disabled ps on ath9k

The patch titled "ath9k: Add new file init.c" shuffled some code
around but in dong so for some reason also removed the revision
check for disablign power save. Add this revision check again
so we can get power save re-enabled again by default on cards
newer than AR5416 and AR5418.

$ git describe --contains 556242049cc3992d0ee625e9f15c4b00ea4baac8
v2.6.34-rc1~233^2~49^2~343

This patch has fixes for stable kernels [2.6.34+].

Cc: stable@kernel.org
Cc: Paul Stewart <pstew@google.com>
Cc: Amod Bodas <amod.bodas@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>