mac80211: fix two issues in debugfs

mac80211: fix two issues in debugfs

Not in trees above 2.6.27 as it is fixed differently in .28.

This fixes RHBZ 466264, whenever the master interface is
renamed this code would BUG_ON. Also fixes a separately
reported bug with the debugfs dir being NULL.

This patch is not applicable to the next kernel version
because both these issues have been fixed, the first one
by not having the master interface have a ieee80211_ptr
at all, and the second one by also leaving the function
early.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: John Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>