ath9k: lock reset and PCU start/stopping

Apart from locking the start and stop PCU we need
to ensure we also content starting and stopping the PCU
between hardware resets.

This is part of a series that will help resolve the bug:

https://bugzilla.kernel.org/show_bug.cgi?id=14624

For more details about this issue refer to:

http://marc.info/?l=linux-wireless&m=128629803703756&w=2

Cc: stable@kernel.org
Cc: Ben Greear <greearb@candelatech.com>
Cc: Kyungwan Nam <kyungwan.nam@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Tested-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/recv.c

@@ -533,13 +533,11 @@ bool ath_stoprecv(struct ath_softc *sc)
 
 void ath_flushrecv(struct ath_softc *sc)
 {
-	spin_lock_bh(&sc->rx.pcu_lock);
 	sc->sc_flags |= SC_OP_RXFLUSH;
 	if (sc->sc_ah->caps.hw_caps & ATH9K_HW_CAP_EDMA)
 		ath_rx_tasklet(sc, 1, true);
 	ath_rx_tasklet(sc, 1, false);
 	sc->sc_flags &= ~SC_OP_RXFLUSH;
-	spin_unlock_bh(&sc->rx.pcu_lock);
 }
 
 static bool ath_beacon_dtim_pending_cab(struct sk_buff *skb)