[PATCH] libertas: fix removal of all debugfs files

rmmod did not remove /sys/kernel/debug/libertas_wireless/eth1/
subscribed_events/high_snr. After I fixed this, I noticed that
it also didn't remove /sys/kernel/debug/libertas_wireless/eth1
as well.

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>