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 6d318e15cfaa2f237d097dbab811d8a69fe6b58c
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>