mac80211: fix queue constant confusion

In commit 31ccc476b77234f6afb3 (mac80211: QoS related cleanups) I
accidentally changed these to use IEEE80211_MAX_AMPDU_QUEUES twice
which obviously is wrong, it should be IEEE80211_MAX_QUEUES once.
Currently harmless as they're both the same value anyway.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>