libertas: stop debugfs code looking at cmdpendingq

It doesn't need to wait until no commands are pending anyway -- it only
needs to wait until the scan is finished.

We can hopefully find it something else to wait on too -- it's the only
user of the cmd_pending waitqueue.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>