ath9k: Fix power save usage count imbalance on deinit

ath9k: Fix power save usage count imbalance on deinit

While unloading the driver, the ps_usecount is incremented
before configuring gpio registers in deinit_device.
But it is failed to restore the ps_usecount after that.
The problem is that the chip is forcibly moved to FULL SLEEP
by radio_disable when mac80211 is reporting as idle
though ps_usecount is not zero.

This patch retores ps_usecount properly and ensures that
the chip is always moved to full sleep only if ps usage
count is zero which also helps in debugging deadbeef on
multivif case. And also fixes the following warning.

ath: DMA failed to stop in 10 ms AR_CR=0xdeadbeef AR_DIAG_SW=0xdeadbeef
ath: Could not stop RX, we could be confusing the DMA engine when we
start RX up
------------[ cut here ]------------
WARNING: at drivers/net/wireless/ath/ath9k/recv.c:536
ath_stoprecv+0xf4/0x100 [ath9k]()

Cc: stable@kernel.org
Cc: Paul Stewart <pstew@google.com>
Signed-off-by: Rajkumar Manoharan <rmanoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>