Staging: line6: fix up some sysfs attribute permissions

They should not be writable by any user

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Markus Grabner <grabner@icg.tugraz.at>
Cc: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>