ath9k: Fix ath9k prevents CPU to enter C3 states

This is a backport of upstream commit 0f5cd45960173ba5b36727decbb4a241cbd35ef9.

The DMA latency issue is observed only in Intel pinetrail platforms
but in the driver we had a default PM-QOS value of 55. This caused
unnecessary power consumption and battery drain in other platforms.

Remove the pm-qos thing in the driver code and address the throughput
issue in Intel pinetrail platfroms in user space using any one of
the scripts in below links:

http://www.kernel.org/pub/linux/kernel/people/mcgrof/scripts/cpudmalatency.c
http://johannes.sipsolutions.net/files/netlatency.c.txt

More details can be found in the following bugzilla link:

https://bugzilla.kernel.org/show_bug.cgi?id=27532

Signed-off-by: Thomas Bächler <thomas@archlinux.org>
Acked-by: Mohammed Shafi Shajakhan <mshajakhan@atheros.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>