ath9k: fix regression which prevents chip sleep after CAB data

The patch:

commit 293dc5df
Author: Gabor Juhos <juhosg@openwrt.org>
Date:   Fri Jun 19 12:17:48 2009 +0200

    ath9k: remove ath_rx_ps_back_to_sleep helper

    This helper only clears the SC_OP_WAIT_FOR_{BEACON,CAB} flags.
    Remove it and clear these flags directly in the approptiate
    places instead.

    Changes-licensed-under: ISC
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

introduced a regression which forgot to lift the beacon flag
after we received all broadcast and multicast data. This meant
we never went to sleep consuming about ~650mW on idle. This pretty
much broke power save completely.

This patch has fixes for stable kernels [2.6.32+].

Cc: stable@kernel.org
Cc: Paul Stewart <pstew@google.com>
Cc: Sameer Nanda <snanda@google.com>
Cc: Gabor Juhos <juhosg@openwrt.org>
Cc: Amod Bodas <amod.bodas@atheros.com>
Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>