mac80211: fix update_tkip_key() documentation about the context

Johannes noticed that I had incorrectly documented the context of
update_tkip_key() driver operation. It must be atomic because all
RX code is run inside rcu critical section.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Kalle Valo <kalle.valo@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index f56d6f4..f64402f 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1489,7 +1489,7 @@
  * @update_tkip_key: See the section "Hardware crypto acceleration"
  * 	This callback will be called in the context of Rx. Called for drivers
  * 	which set IEEE80211_KEY_FLAG_TKIP_REQ_RX_P1_KEY.
- *	The callback can sleep.
+ *	The callback must be atomic.
  *
  * @hw_scan: Ask the hardware to service the scan request, no need to start
  *	the scan state machine in stack. The scan must honour the channel