staging: wfx: fix AC priority

staging: wfx: fix AC priority

In order to work properly all the queues of the device must be filled (the
device chooses itself the queue to use depending of AC parameters and
other things). It is the job of wfx_tx_queues_get_skb() to choose which
queue must be filled. However, the sorting algorithm was inverted, so it
prioritized the already filled queue! Consequently, the AC priorities was
badly broken.

Fixes: d141cb7b1f860 ("staging: wfx: change the way to choose frame to send")
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200529121603.1050891-1-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>