ath5k: fix Security issue in DebugFS part of ath5k

http://bugzilla.kernel.org/show_bug.cgi?id=12076



Remove any write access to groups and others, only keep write permission
to its owner, usually only root user.

Reported-by: Jérôme Poulin <jeromepoulin@gmail.com>
Signed-off-by: Cheng Renquan <crquan@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>