ath5k: Don't wake internal queues

We should only wake up queues which mac80211 knows about (queues 0-3). We have
another internal queue ("CAB", queue number 6) which we use for power-saved
frames. When transmitted frames are processed from this queue, we have to make
sure we don't bother mac80211 with waking a queue it doesn't know about.

this fixes:

WARNING: at /home/br1/ath/wireless-testing/net/mac80211/util.c:275
  __ieee80211_wake_queue+0xd6/0xe0 [mac80211]()

Signed-off-by: Bruno Randolf <br1@einfach.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>